What does ack-ack ack-ack Ack Ack mean?

ack-ack ack-ack Ack Ack meaning in Urban Dictionary

-Anti environment flak, term used in World War I. Noun: Stemming from slang for "anti-aircraft" - A person who shoots someone else's idea, thought, or feeling down. hidden nickname for marijuana, esp. whenever used in combination with parents/police present. Could also be used as a verb (See instance below)