Agree (regretfully) that the amoeba-brained twerp will likely get off with little if any punishment (I hope I am wrong). Got me thinking though, what would it take for you, as a pax witnessing this, to get involved, or would you steadfastly refuse to (which is probably the sensible option). I'm talking this situation specifically where apart from a shirt-grab there is no physical attack on any crew or pax, just a bunch of verbal abuse, and an apparent refusal to follow crew directions.
Despite a reluctance to 'get involved' and an inability to fight my way out of a wet paper bag, at some point I'm sure the temptation would be bubbling very close to the surface. Just to 'calm him down'.
But no doubt I'd just request extra popcorn.
Thinking about this if I was on the flight and had known who he was(unlikely with my knowledge of celebrities) I would have been tempted to go up to him and invite him to hit me saying I would appreciate his father paying me a million +.