What is Marshmallow Surprise?
1.
A sex act where midway through intercourse the male defecates into a sock and shoves it into the females mouth.
guy: dude I gave my girlfriend a marshmallow surprise
guy2: nasty
See
2.
A seemingly delicious
"Do we have marshmallows for the campout tonight?"
"No, Kara took them all so she could make Marshmallow Surprise."
See