Currently I have friends and some acquaintances who I've managed to stay in contact with. My normal procedure is to panic and hide when people express an interest in being friends outside of class etc.
Avoidant reasons:
--I don't want to bother them/I shouldn't waste their time
--I don't want to wear out my welcome
--They'll think my idea for what to do is dumb (I tend to let other people do the inviting/planning for this reason)
--They might invite other people and I won't be able to be myself
--If it's an old friend, they might interrogate me about what I'm doing now and then criticize me
--I'm testing them to see if out of sight=out of mind
--I fear that they're only inviting me out of pity so I try to save them the trouble
--The good ol' "If they get to know me better they won't like me anymore"
--I don't drive (because of avoidance-related crap)
Non avoidant reasons (more anxiety related):
--It's too hot and I sweat too much
--My hair/clothes/appearance aren't "right", thus I'll be criticized or mocked (only a real threat with other females, but I fear it with my male friends as well)
--I'm an introvert anyway
--When I'm depressed, I don't see the point/don't have the energy for putting up the happy, funny facade