When you go to tuck in your significant other, but then get engaged in a round of sex after tucking them in.
ferdaayz: yo where's supremeclientele44?
Hudson: he's probably just tuck fucking his girl again
ferdaayz: ahhhh the patented tuck fuck
The act of fucking a bitch and then tucking your dick between your legs to make her laugh.
*after finishing guy stands up*
Guy: Hey babe look
Girl: *looks and sees he has tucked his dick in between his legs*
Guy: *laughs*
Girl: *got fucked and then saw it tucked*
= Fuck n’ Tuck