I think it's a fetish for some people, they get to that boundary where nothing else pleases them ( normal sex ) & they gotta ease the urge with a hooker.
...he wanted some of that brown sugar.
...for a slice of the devils pie.
....had to do it one mo gin.
....he was tryin to do it left to right.
ok, ok, Im done LOL
but for real, dude has lived quite the life:
http://en.wikipedia.org/wiki/D'Angelo