Whoring the boat
A term referring to a night of sexual intercourse with one's girlfriend and then sleeping all night. Usually used in a detrimental or playful manner by friends who obviously want to do something more interesting. Especially pertinent in the case where that particular friend's girlfriend is on the larger side.
"So why isn't Jonny here tonight?"
"Oh, he's whoring the boat all night again."
"Oh, he's whoring the boat all night again."