All I can suggest is that if he does it again sometime make sure you both get really drunk first.
Then tease and hit on him all night. Walk up behind him and grab his boobs, call him baby, slap his ass playfully, things like that as long as he's playing along with it. If he acts weirded out then just laugh and back off.
If he likes it play along a little more. Joke about a ffm with another girl right in front of hin, things like that. Introduce him to people as your girlfriend.
The next day joke about some drunk slut at the party that wanted you bad!
