To lose really badly in a race, usually as it applies in motorcycle and car racing. Someone who has been gapped has lost a race so badly that he or she should strongly consider finding a new hobby.
Beating someone by half a car length is not a "gap." You must beat someone by an absolutely humiliating distance, like two or more bus lengths.
Joe thought he could take on Greg's corvette, but he got gapped and everyonesaw.
A sex act where the male pulls back the foreskin from his uncircumcised penis, scrapes out the dirt and crust, sniffs it, and rubs it across his partner's upper lip.