This can only be done in the missionary position during anal intercourse. You (gently) insert your fist into her vagina until you feel yourself inside her ass, then you proceed to masturbate using her colon like a sleeve. Believe me, this can be done.
My Ex. Fist assist, last night I gave her the ol' fist assist.
by StrangeO July 22, 2009
Can you define these popular missing words?