One opener I've been using recently which has worked for me so far - approach the group (can only be used in a bar or pub type venue) and say 'is there anything I can do to make your experience here that little bit better?' The usual reply is 'yeah, get us a free drink', or 'do us a dance'. I usually reply with 'well I would buy you a drink, but I think the barman fancies me so I'm trying to avoid him. Or if they ask you to be their dancing monkey I grab my balls and do the Micheal Jackson 'oowwwww', which always gets a laugh, especially with groups of drunk girls.