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1.
given to unintelligent decisions or acts : acting in an unintelligent or careless manner
Obama:"Cambridge police acted stupidly in arresting somebody when there was already proof that they were in their own home."
by steve14 July 23, 2009
 
2.
some one whos verry dumb or acts dumb
your bro is acting very stupidly
by the heatons 1 December 28, 2008