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1 definition by concernedhoya

Big Mouth Make-out.
You're at the bar late, you've been talking to a boy/girl for a while, you both know what's going to happen, but you're a little tipsy so you're not sure the mouths are going to match up, so you just plunge into the BMM without a care for who sees it.

Johnny didn't care who saw it; he and that girl were just BMMing last night.
by concernedhoya January 08, 2010