A party pooper is the one who's always ruining our positive day.  Thanks for nothing, PartyPooper. He or she takes all our energy from us by pooping the party or pooping the day. It can even cause a WikiSmell.

''Cheer up, thanks for everything. --PartyPooper''
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'''Dijkstra''': "I guess they considered me what you Americans call a pooper-scooper."

'''MPJ''': "Party pooper". 
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See: http://www.waysys.com/ws_content_al_isd.html

CategoryIdiom