Idea
The Pun Tyrant
If we’re talking about “the” “biggest” red flags, then the answer is the boring one: Stuff like people sending you weird links, or trying to show you stuff while telling you not to tell anyone, or making offers that are too good to be true while requiring stuff from you that could get you trapped, and in addition to that type of stuff, the kind of manipulative, shady or abusive behavior that would be a red flag in real life as well.
Bringing it down to more personal terms, there are many red flags for me, but I tend to be picky to begin with. Some of the things that come to mind right away are for instance when someone says they are “willing to do anything” or “ok with anything/everything”. There is no such thing as a person without preferences, so someone who says that is either not being truthful or simply lacks self-awareness. Of course, compromising is a part of working with other people, but either you’re going to start going “Ah wait actually I can’t do that” (aka telling your preferences just with extra steps and more frustration) or you’re there just to put up with whatever, or in other words, rather than being passionate about something and it not being everyone’s cup of tea, you end up being mellow at everything all the time. Whichever the case, it’s a bad time incoming, and that’s assuming the person in question doesn’t just get bored immediately as they realize they actually don’t like the idea after all.
Another big red flag for me is unspoken rules and unwillingness to work around them. This mostly applies in GMs, though it may happen with a 1x1 partner too. If something comes up in discussion or the character creation process that is a rule of the roleplay that was never stated (explicitly or clearly implied), and furthermore there is either no way to work around it or the GM refuses to try to find a way to accommodate the core of what I was going for without breaching the rule, then I can’t trust that GM to not suddenly turn around and wreck something more significant with another unwritten rule. Not only is it something that can utterly shatter my motivation, it also breaks that element of trust.
Politics and very specific IRL matters such as specific conditions is yet another thing I don’t want to touch with a hundred foot stick. I am not interested in getting involved in time bombs and topics people tend to be excessively sensitive about. I’ve lost friends over things like refusing to dogpile on someone. Even if the OOC doesn’t degenerate, I like to keep a good separation between fiction and reality and to not have to constantly handle things with kids gloves. I want to explore and share ideas, to tell stories, to have fun with this, and I don’t think I can do that when people go in with the impression that this is meant to portray reality. (It should be noted though I am willing to dive into topics that even I am sensitive about. Those who know me know I don’t shy away from a good civil discussion/debate. But exploring a sensitive theme is something I am not willing to do unless I really trust that the person understands the boundaries of story and reality, of character / narration and opinion, and holding or entertaining a different view and personally attacking someone. Such themes in roleplay are for make things more fun or interesting, and in cases of more serious exploration for reflecting different aspects of it.)
Those to me are the main things that come to mind. There are many red flags for me like I said, so there may be more I would consider even more serious if I had them in mind but right now, those are the ones that I thought of.
One last thing I would like to note is that lately I’ve been seeing something I normally consider a red flag that I might have to re-evaluate: Lore dumps in the interest check. It’s a case of poor priorities, like putting a character as the focus of the group interest check, that shows a bigger focus on a character or the world than the good of the RP. This is or was a potential indicator of some poor GM behavior, in the case of the character for instance being that GM character that ends up having everything focused around them, and in the case of the world the GM constraining everything about the characters.
However, lately it’s become more of a default. Rather than being an intentional, deliberate choice, I think it’s started to become taken as just normal to dump several paragraphs of backstory on the setting before introducing the premise. Indicators are something I took from experience, but when they become normalized I feel they may not be the red flags they used to be. After all, it’s not the GM who is too focused on the lore that they will dump it in without thinking if it will be appealing to read through or not - it’s just your regular run of the mill GM just doing what they think is the normal or expected thing to do.
Bringing it down to more personal terms, there are many red flags for me, but I tend to be picky to begin with. Some of the things that come to mind right away are for instance when someone says they are “willing to do anything” or “ok with anything/everything”. There is no such thing as a person without preferences, so someone who says that is either not being truthful or simply lacks self-awareness. Of course, compromising is a part of working with other people, but either you’re going to start going “Ah wait actually I can’t do that” (aka telling your preferences just with extra steps and more frustration) or you’re there just to put up with whatever, or in other words, rather than being passionate about something and it not being everyone’s cup of tea, you end up being mellow at everything all the time. Whichever the case, it’s a bad time incoming, and that’s assuming the person in question doesn’t just get bored immediately as they realize they actually don’t like the idea after all.
Another big red flag for me is unspoken rules and unwillingness to work around them. This mostly applies in GMs, though it may happen with a 1x1 partner too. If something comes up in discussion or the character creation process that is a rule of the roleplay that was never stated (explicitly or clearly implied), and furthermore there is either no way to work around it or the GM refuses to try to find a way to accommodate the core of what I was going for without breaching the rule, then I can’t trust that GM to not suddenly turn around and wreck something more significant with another unwritten rule. Not only is it something that can utterly shatter my motivation, it also breaks that element of trust.
Politics and very specific IRL matters such as specific conditions is yet another thing I don’t want to touch with a hundred foot stick. I am not interested in getting involved in time bombs and topics people tend to be excessively sensitive about. I’ve lost friends over things like refusing to dogpile on someone. Even if the OOC doesn’t degenerate, I like to keep a good separation between fiction and reality and to not have to constantly handle things with kids gloves. I want to explore and share ideas, to tell stories, to have fun with this, and I don’t think I can do that when people go in with the impression that this is meant to portray reality. (It should be noted though I am willing to dive into topics that even I am sensitive about. Those who know me know I don’t shy away from a good civil discussion/debate. But exploring a sensitive theme is something I am not willing to do unless I really trust that the person understands the boundaries of story and reality, of character / narration and opinion, and holding or entertaining a different view and personally attacking someone. Such themes in roleplay are for make things more fun or interesting, and in cases of more serious exploration for reflecting different aspects of it.)
Those to me are the main things that come to mind. There are many red flags for me like I said, so there may be more I would consider even more serious if I had them in mind but right now, those are the ones that I thought of.
One last thing I would like to note is that lately I’ve been seeing something I normally consider a red flag that I might have to re-evaluate: Lore dumps in the interest check. It’s a case of poor priorities, like putting a character as the focus of the group interest check, that shows a bigger focus on a character or the world than the good of the RP. This is or was a potential indicator of some poor GM behavior, in the case of the character for instance being that GM character that ends up having everything focused around them, and in the case of the world the GM constraining everything about the characters.
However, lately it’s become more of a default. Rather than being an intentional, deliberate choice, I think it’s started to become taken as just normal to dump several paragraphs of backstory on the setting before introducing the premise. Indicators are something I took from experience, but when they become normalized I feel they may not be the red flags they used to be. After all, it’s not the GM who is too focused on the lore that they will dump it in without thinking if it will be appealing to read through or not - it’s just your regular run of the mill GM just doing what they think is the normal or expected thing to do.
I just can't. 
