... believe the women to be in the right?
Not sure what you mean, the women I've known tend to be
in the bedroom or
in the kitchen, I don't have any rooms call 'right'

.
Personally I think
LOAMs answer was the most reasonable to be followed up by reporting to the police if that does not resolve it.
Alternatively;
As he like to ambush your GF coming out of the ladies toilets, take a wig and matching outfit and at the end of the night when he is likely to be good and drunk, nip in to the ladies and get dressed up like your girlfriend, come out and get grabbed by him at which time plant a big wet kiss on him whilst your girlfriend takes a picture and just to make sure the expression suits the moment, grab hit happy sacs in a vice like grip and squeeze hard.
Don't like that one ?... Ok what about;
Suggest going for a trip to France by ferry saying you want everyone to be friends. Let the customs over in Calais know he is coming so they can be ready to greet him with some handcuffs and a pair of disposible rubber gloves.
Nah... ok then, here is another;
When having your man to man chat slip some laxative in his beer. Don't overdo it, don't want to kill the guy, just help him to cleanse from the inside

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On a more serious note...
How likely are her friends to lie for her ?.
Explain to her you are very upset by the way he is treating her and it is having an impact on your relationship and so she needs to tell him outright to leave her alone or she will go to the police. If he continues then she needs to go to the police. No point making the threat and then not following through. If she refuses then just like transformers, there may be 'more than meets the eye'.
RB