Playing with your ass, exploring that forbidden hole, doesn't have to be an act of humiliation. In fact, it shouldn't be. There's so much enjoyment to experience from anal masturbation, and the taboo just makes it that much more exciting.
She's running late on reports, when you, the Boss, cum into to sign off on them. But when you drop a pen beneath her desk and go to grab it, you accidentally look up her skirt and see her cock!