Our uni's just had a rubix cube night. Come wearing 6 different colours, at set times a buzzer goes off and you have to swap one item of clothing with someone, and end up with all clothes the same colour.
We had Geeks & Gangers on tuesday night which worked pretty well...
All the blokes have to do is slick back their hair and wear dark glasses + leather jacket all night.A good way to keep it open, while still having a theme is to pick a letter as theme. For instance a 'C' party can have crayons, courtesans, colons (the punctuation) etc. People can make a word fit what they want to dress as keeping all happy.
What the hell is a ganger?
Anyway just do pimps and ho's so you can get the ladies to all dress up hotAll the blokes have to do is slick back their hair and wear dark glasses + leather jacket all night.
Hmm...clerics.
You'll get lots of bishops and popes, but the more adventurous could find something from one of the dozens of other religions.