Funnyman Ben Stiller wasn't laughing after his encounter with monkey actor CRYSTAL on the set of his new movie A NIGHT AT THE MUSEUM - because she slapped him silly. And, to make matters even worse for the Meet The Fockers star, he wasn't allowed to retaliate - and had to take his angst out on the ape's puppet double. Stiller says, "She wears a diaper and resents the fact that she can't control herself so she has all this pent-up aggression. "She gets to hit me in one scene but I think there's some animal protection rule, whereby you can't hit a monkey back - because they'll bite you or something. "I couldn't hit her back, so, when it came time for my close-up I'd get the monkey puppet to hit which was not satisfying so I have unresolved issues with Crystal. If I saw her now I would still want to smack her. "(In the scene) she could hit me as hard as she wanted and was encouraged to hit me hard. The trainer was behind me, yelling, 'Smack the crap out of him!' It was really annoying."