I would take note but let it go. Sometimes in these sorts of situations what is important isn't what is said, but what isn't being said. There's usually a motive and reason behind everything people say and do. I have my own opinions here, but what do you think these reasons and motives are?
Has anything changed in the relationship between you and your mother since this event?
I say take note but let it go because this could be a one off due to peer pressure, in a club, after a couple of drinks. One of the effects of alcohol is that people say and do stupid things, usually when they're with friends.
But then again it might not, and if so then it will manifest itself again at some point at which point you could raise the issue and discuss it further.
I'm sorry you had to go through this.