When you're doing a girl from behind, you cum in her hair and then arrange her hair into a Donald-esque comb-over, then when she turns around in approval, you smack her and yell, "you're fired!" If you can do the snake hand, arm motion that the Donald does on The Apprentice, it's a bit more effective.
There was this one time, me and my girl were doing it and I accidentally came in her hair, then tried to get it out. But it just ended up looking like Donald Trump's comb-over. It was pretty fuckin funny.