The opposite of fun.
My date last night was horrible! No matter what I suggested, she just didn't want to do anything! She was so antifun!
by Babo Sang Pyo October 30, 2005
Someone who is absolutely hell-bent on not having a good time or, more importantly, has a great way of curtailing others having a fun time
My boss wouldn't let me have an hour off to catch the game. He really is the anti fun
by Neil73 March 26, 2007