Romantic

When dating:

• treats service staff badly,
• tries to decree what I will or will not eat/drink,
• attempts any form of manosphere shit like "negging",
• spends the entire date talking about themselves,
• spends a lot of the time saying disparaging things about other people.

Sexual

• consistently selfish,
• doesn't pay attention to body language,
• doesn't pay attention to verbal feedback like "I don't like that",
• pays attention to verbal feedback ... by trying to tell me what I should or should not like,

Interpersonal

• always talking shit about other people not present (because you know they're doing the same about you when you're not around!),
• takes but never gives,
• borrows but never returns,
• won't help me move the body.

Social

• suspiciously non-diverse in makeup (ethnically, religiously, politically, etc.).

Business/Employment

• poor representation of women and minorities,
• dismissive of to hostile toward attempts to correct that representation,
• brusque/rude HR or management,
• disorganized HR or management,
• strict dress code,
• religious symbolism of any kind displayed in shared spaces.

My biggest red flag isn't some behavior in another. It is my instant attraction to someone. My picker is broken....

I don't date / haven't dated, so I have no skill or experience with that - but with new people I meet there are all sorts of warning signals / red flags I get, mostly there are just different tropes or types of people:

• people who suffer from over-responsibility / Atlas complex - usually someone who was parentified by negligent parents growing up and now they have a dysfunctional relationship with a dependent partner / spouse or friends
• people who believe in ghosts, gods, religions, spirituality, etc. (whether New Age or organized religion) and are usually more likely to be victimized by scams, pyramid schemes, cult leaders, and pseudoscience health fraud; a lot of these people suffer from positivity bias and fail to think critically and recognize threats, particularly from within their trusted in-group
• drug abusers, for whatever reasons - alcohol and cigarettes are common because they're socially promoted and culturally tolerated; related: gambling, "sex addiction", risk-taking behavior (adrenaline junkies)
• workaholics - basically their whole life is work, most of their friends are only made at work, they make unreasonable sacrifices for work and have a hard time drawing boundaries, they might work on weekends, in the evenings, and basically are thinking about work all the time; often this is a form of escapism, and usually they neglect their partner / family / home life

I could keep thinking of more, there are a lot. Basically everyone I know has some major problem or another. I'd rather just stay home and interact with people anonymously over the internet, it's a lot safer.

Anyone that only focuses on themselves in the relationship. Relationships are a two way road. Both people should care for one another and be interested in their life. I just read an article where a liberal woman dated a bunch of conservative men, and they categorically only care for themselves and didn't even ask her about her life, even over multiple dates. Huge red flag.

Also, anyone that destroys a bathroom regularly and doesn't clean up after themselves. That sort of thing can be improved over time, but it's a sign that they're probably a dirtbag. Personally, I'm just not compatible with that.

Some good suggestions already here, so I'mma put up my own queer fem experience;

• Calling stuff "woke" in a negative sense. It's a pretty damn big code for "I hate people and blame my own insecurities on them". They might view us as "snowflakes", but when we get criticised, we actually tackle it (when it's constructive criticism), when they won't even take the latter one.

• Being rude and verbally/physically violent, insisting. Being civil, compassionate, and accepting is a sign of better personality.

• Not letting me finish my sentences or talking in noisy environments. Wait your damn turn or until I can understand you!

• Smoking (don't care which type). I'm not going for someone who doesn't take care of themselves and also doesn't do that for others.

• Being a self-proclaimed "sigma", "alpha" or whatever. Again, insecurity and toxic masculinity. Besides, real "sigmas" and "alphas" don't need to tell they're one. They emanate it by their confidence, kindness and compassion towards others.

• Dismissing science, eg. being an antivaxxer. You're setting up people for abuse that way, as it hurts peoples' health, and spreads harmful falsehoods.

• Only caring about sex. I'm a friend/partner, not your prospective fucktoy.