The Kiss On The Lips was a party thrown by Blair in Pilot.
Jenny wrote out the invitations as a deal with Blair where she could attend if she did so. The party was held at a Manhattan club and most of Constance/St. Jude's student body attended. During the party, Chuck meets Jenny and attempts to have sex with her, but doesn't when Dan and Serena stop him. Nate leaves after becoming annoyed with Blair's need to control him around Serena and watches from across the street.