Red signs you've noticed in partners that made you want to slap your past self?

I have a good one, just popped back into my head and inspired this. We were watching a movie where a wife cheated on her husband and I say "Damn, what a horrible person". And she just loses it, going off on how "that's such a misogynistic thing to say" "how do you know what SHE was going through" etc. I tried to laugh it off because she was hot and it was early in the relationship and I'm stupid but I'll give you one guess why that particular relationship ended lol.

Anyone else have some relationship red flags, major or subtle, that just made you want to go back and slap your past self?