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2.
Noun: Stemming from the slang for "anti-aircraft" - A person who shoots another person's idea, thought, or feeling down.
Person 1: "How about Joe's Bar tonight?"
Person 2: "How about no?"
Person 1: "You, sir, are an Ack-ack..."
by DRoseMVP1235 May 02, 2011
 
1.
-Anti air flak, term used in World War I.
Ack-ack downed more planes than dogfights during the First World War.
by syrianarab May 24, 2005
 
3.
inconspicuous nickname for marijuana, esp. when used with parents/police present. Can also be used as a verb (See example below)
N.)- Yo lets go get some of that dank ack ack from that kid down the street.
V.)- Im gonna go take a cruise and ack it up if you wanna come.
by ThaStonedGecko January 23, 2007