This sounds like fun! Hmm… what about..
Dress completely in one colour.
Wear only clothes that you haven’t worn in over a year
Challenge yourself to wear something you think is unflattering and try and make it look good
Dress up like a cartoon character (eg Daria, Misty from Pokemon, etc..)
Dress like you are from another time period (eg from the 1900s :P)
Wear heaps of clashing prints/patterns.
Wear double denim
Dress like you just stepped out of the 1980s
Find an old photo of you when you were a kid and try and recreate the outfit you’re wearing!
You could also pick days to dress in a certain style- eg Boho, Lolita, Punk…