a metaphor to describe when a person creates a diversion for a friend in order to trick the person so that his friend can get somewhere with a girl he's with. the exit describes getting to the end point and the ramp is the time the person is taking to create the diversion while the friend slips by with the girl.
bob pulls into the street with jen and greg. dave and a girl are in the other car trying to get into the house against the will of jen since dave is her son and she is against one night stands. greg then makes conversation with jen and bob to create the diversion while dave and the girl slip into the house undetected and do what they were destined to do. that is an exit ramp