On HK guns the charging handle can be locked up in a little notch. When you "slap" the handle back down it loads a bullet in the chamber. Hence the term HK slap.
When you HK slap a wal-mart airsoft mp5... the handle will break off.
To senselessly trounce a man's forehead or cheeks with one's chafed scrotum after a night out on a trannychase. Otherwise known as a victory slap, to prove to other trannies that Briggsy has made a kill. Has also been referred to as territorial marking.
Denzil: Have you noticed all the trannies with bruised faces?
Roland: Yeah. Looks like Briggsy's being dishing out some more Briggsy's Turkey Slaps.