Doctor Bob had sex
Doctor Bob had sex with one of his patients and had felt guilty all day long.
No matter how much he tried to forget about it, he couldn't. The guilt and sense of betrayal was overwhelming.
Every once in a while, however, he'd hear that soothing voice, within himself, trying to reassure him: "Bob, don't worry about it. You aren't the first doctor to sleep with one of their patients, and you won't be the last. And you're single. Let it go."
But invariably another voice would bring him back to reality: "Bob, you're a veterinarian!"