When you have anal sex with a partner (doggy style), then you remove your penis before you cum, spit on the partners back so they think you have unloaded your giant load of mainly goodness on their back. Then your partner will then look back and you cum right in their face.
Yeah dude i gave her a nice back wax.
Yeah she thought i let it go, untill she realized i back waxed.
Yeah I back waxed and she got pissed, because she recieved the ultimate facial.
Yeah, my gay male partners usually ask me to back wax because they like the surprise.