I've earned a few "spite bites" in my time. If I insist that Timber steps up, when he is doing something he wants to do that I don't want him to do or something dangerous, he will bite after stepping up. I just put him in the cage for a time out when that happens. I've also had to use the dreaded towel to force compliance (like getting him in the carrier to go to the vet). I always use it as a last resort, but you do what you have to do. During the first six months or so of our relationship, I felt like incidents like this caused a setback. Now that he trusts me, he doesn't seem to hold a grudge or get upset for any length of time.