Theme Parties

My friend's are whining that we need a get together. I agree - a get together is in order. However, we don't really have a real reason to get together for none other than to see each other. Typically - Doug and I host events such as the superbowl, Colts/Pats game, Christmas party....but it's not Christmas time, and it's not football season - so, what's the excuse we can use to host a get together?? 

Item number 15 on my list is to Host a Theme party! That's the excuse I'm going with. However - what theme should I go with?? I really have no clue. Suggestions?