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2.
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
 
1.
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