Wow lots of people hating on the OP's friend. Maybe they are the type to grab asses? heh.
I think the guy who got his ass kicked had it coming. In northern Ontario they would do a lot more than that--they'd take you in a mine and put you behind a big rock
So many people are quick to say "OMFG SERVES HIM RIGHT SUE HIS AZZ!" but why? Too many rights nowadays for the perps...whatever happened to victims rights? So what the girl wasn't giving the guy blowjobs, there is still some decency around that suggests he should protect her.
Of course going to the bouncer would have been the best idea. But he was in the heat of the moment. Hey maybe you can get off like cops who beat/shoot people after chasing them because they are not thinking clearly/"enraged" or whatever they call it
And yes, have the girl threaten that she will go after him. A sexual offense would look very bad on his record.