A bowling alley is a common bowling like sexual position reference. It is the act of taking the males nutsack and starting from the toes of the male/female beginning to rub the sack up the person's body until reaching the mouth where the nut sack is inserted.
The name is a reference to a bowling alley due to the fact as the nuts equal in meaning of a bowling ball and the mouth not clearly but referenced to the pins or gutter.
Girl: WTF is a bowl...
Guy: -rubs- STRIKE!
-later that day-
Girl: what the hell was that you did back there?
Guy: that was the bowling alley