'You're supposed to sip it.'
Gail: "Well, it's like a shot."
Doug: "No. You're supposed to sip it."
This exchange tells quite a bit about the brother-sister relationship, and approaches to life. Unless of course, you just take the scene at face-value and think it is just some meaningless club small-talk about booze in a danceclub, where the unattached brother and boyfriendless sister would rather be next to each other than dance with others.