So I’m rewatching the second season of American Crime Story about Andrew Cunanan and the Andy vibes are off the fucking charts. It’s the same predicament you mention, he’s extremely offputting in a way you can’t quite verbalize. His ingratiating behavior reads as desperation and probably eighty percent of his interactions are people just kind of tolerating until they can run away.”Uh huh, that’s cool…how fun! I’ve gotta run, bye!!”

However, for the people Andy ensnares, that ingratiation speaks to them in some form or another.
Either genuinely, because they don’t see that he’s just a chameleon telling people what they want to hear or what he thinks they want to hear (all the while painting himself as the most interesting, intelligent, well versed individual in whatever situation he’s describing) or maybe out of some sort of misguided pity. Like an “aw, you look like you need a win, I’ll listen to you and build you up a little bit” sort of deal.