On the off-chance that someone knowledgeable here still plays this game...
My romance sim had three bolts with the cow mascot, so I let her romance him after she graduated and went back to the main hood. This turned out to be a mistake, as now the cow mascot strolls by every single day and invites himself into the house to engage in naked hottubbing, regardless of the fact that I have localwalkby installed and APO set up on the lot to ban "hostile"s and "disruptive"s (I imagine the cow mascot must fall into at least one of those categories). It was kind of amusing the first couple days, as my sim's mother used to beat up the cow mascot in college and is more than happy to return to her pastime, but now I'm getting kind of annoyed. Anyone know why this is happening, and how I can stop it?
The best answer I've seen to this is that the Uni Mascots and some of the other NPCs are basically psychotics//neurotics and you invite them into your family at your own risk! Many have non-standard personalities and some appear to be corrupted. Having married a Sim to the Repoman, several to maids and a couple to Uni Mascots, I can agree with this. But they are fun.