Swag is the semen from when two men have anal sex and the 'bottom', who's receiving the sperm from the other, keeps the semen (swag) inside him before showering. If someone says they have 'swag' they mean they've recently engaged in homosexual activities, still have the swag in their rectum and haven't yet showered.
by Harlequinist/Sluth December 20, 2013