A theme party in a dorm might be kinda difficult but graffiti parties are awesome, we had one the other week with some friends and it was a blast, just play techno all night long, get a ton of black lights, splatter paint the wall in highlighter paint and have a lot of fun.
Also some more ideas
Red Neck Trailer bash,
GI joes,
Cowboy's and cowgirls
Snowpants or nopants
Mountain man and ski bunnies
... the list can go on forever
A great theme to do that might actually would work in the dorms would be an, - Around the World party
where you have each room be a different spot in the world (Ireland, Britain, Australia, USA,, Russia, etc) and then each Country has a different drink in the room; Irish car bombs for Ireland, Foster's for Australia, Vodka for Russia, etc. and then you go to the different rooms and try it all, also if your into it you can make one room Jamaica and just smoke there