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1.
Having so much fun you carelessly hit your head hard on something.
Melissa Morris was having so much fun dancing in the club that she got a funcussion by slipping and hitting her head on the bar.
by snowbro780 October 23, 2011
 
2.
A group of Japanese highschoolers in gold shirts having fun playing the drums.
Ichiro and Toyota invited us to do some funcussion, remember to bring your gold shirt.
by MarkMillarLicksGoats July 01, 2013