I don't think it is really.
I was out on Saturday night and this happened to me twice and I simply ignored both girls and carried on as though nothing had happened. At first I thought I might be being a bit harsh at first and that maybe turning round and at least acknowledging them would have been the less twatish thing to do.
When I think about it why should it be acceptable for girls to be allowed to do this and not guys. A tap on the shoulder, or a brush past, or flirty eye contact is perfectly adequate.
Guys aren't always sluts and we don't always like being touched by girls, I could have had a girlfriend for all she knew anyway.
I just don't get this, it really puts me off anyone who does it and I don't see why the rules should be different for girls/guys.