A friend of mine organised a hen recently - They had dinner in Odessa (plenty of cocktails) spent an hour or so in the pool hall on Camden st and then headed to the Gaiety to dance the night away (there's a selection of DH's and bands there) not too out of the ordainary but they really enjoyed it.
How about going to something like this [broken link removed]
or the laughter lounge on the quays? or one of the karoke bars in town
I'll be organising my friends Hen in january and I think it's just going to be cocktails and a Karoke Machine at home and then on to a cheesy night club.