A sexual act that involves a man cumming into another partner's mouth who has a gauged labret piercing. The partner with the piercing then yells "shotgun" and ejects the fluid at the man through the labret.
May also evolve into snowballing.
Shotgunning: Rich orgasms into Jackie's mouth, at which time Jackie jumps up, yells 'shotgun!', and ejects the cum into Rich's face.