Same here. This has been happening since the last patch; there are no mods or CC in my game and I don't want to use them, especially not for something like this. My sim (who has the Loner trait) will autonomously walk up to random strangers and be mean to them, even though she doesn't have any traits that would cause her to do that. She has a circle of 6 friends, including one romantic interest. Literally every time any of them interact, no matter how well the conversation is going, either my sim autonomously chooses a mean interaction or, if I'm being careful to control the conversation, the NPC sim(s) will start yelling or performing mean interactions toward my sim. Yesterday she had all 6 friends over and ended up with hurt/festering grudge sentiments for 2 of them and lowered friendship bars for 2 more.
Romance is impossible at this point because the constant negative interactions from the romantic interest are destroying both the friendship and romance bars. I have to constantly keep an eye on my sim to make sure she isn't autonomously choosing to be mean to everyone, and be careful of where I send her so that she doesn't run into the friends toward whom she has negative sentiments until the cooldown period is over (I know I can remove them with cheats, but what's the point if the next interaction is probably going to cause them to come back?). What makes it worse is that socializing and building up relationships is already difficult in the first place because of the Loner trait, so I feel like all the work I've been doing to get my sim to make some friends has basically been for nothing. At this point I'm probably just going to wait until this is fixed before I start playing again.
