When fisting your partner, using a tightly balled up fist fully insde them, without warning, you yell BANG!! while simultaneously opening your fist, fully extending your fingers, creating the sensation (and possibly similar physical affect) of a grenade going off inside them.
Warning: a
poor manicure
may enhance the
hamburger effect.
Guy: Last night I was fisting a real dead
fish and decided to liven things up with a grenade. She jumped around so much, she almost
broke my wrist.