To cause trouble or to create mischief.
Hey guys, do you have the eggs and paintball guns so that we can run-a-muck tonight?
by mnemonic7 March 05, 2004
when you get engaged to a girl, but decide to take drugs and sleep with any other girl who is available just because it is a special occasion..ie an 18th bday.
rachael:what's this i hear about you cheating on me at that party?

josh:i didn't cheat on you...i just runamuck a bit....it was only coz you weren't around.

rachael:..........what do you mean i wasn't around???? i was in the room next door.......
by ashke July 01, 2010

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