Why is it that videotaping someone makes him lose his inhibitions? Why is it that if I videotape somebody, it makes him lose his inhibitions?
Usually, being observed increases someone's self-consciousness and they control their behavior (which is a problem in ethnographic field studies: the presence of the foreign observer changes the behavior of the native subjects). Usually, this leads to more socially acceptable behavior (no public nose picking) and a self-conscious stiffness.

In a private situation, and especially when under the influence of alcohol, being observed might induce someone to decide to behave more excessive, because that is what is expected and socially acceptable in such a situation. Everybody would be quite bored and disappointed, if pointing a camera at someone while on a party or during a holiday outing would not lead to those in front of the camera doing funny stuff. So in fact, "losing their inhibitions" in front of the camera is exactly the opposite: conforming to social expectations.