....and having a tray of drinks poured on you can be either "battery" or "provocation". As for "theft of services", when the service includes the unordered tray of drinks atop one's head, even the police are unlikely to be willing to make an arrest. There are a number of potential criminal violations which could put the resturant at great risk for potential liabiliy far greater than the cost of dinner.

After all, the resturant certainly has the right to sue for a civil debt.

....as for making a scene in front of clients, what of the clients' perception that their host was a whoosh (anda wet one at that)?