An ambiguous phrase used in a purely contextual manner. Amusing because it means nothing & everything at the same time; use is only limited by the user's imagination. Sometimes used to confuse the uninitiated.
Yo bro, i gotta go punch the muffin (Take a dump)
They were punching the muffin all night (Sexy time)
Tom & Joe were punching the muffin about you (Talking shit)
Punch the muffin bro! (Accompanied by the fist touch, high 5, etc...)
Way to punch the muffin dumbass (Drop the ball, screw up, etc)