On this page of the game guide to Borderlands 2 you will find a detailed description of the side mission titled You Are Cordially Invited: Tea Party. You can begin this quest in the Tundra Express location after the completion of the side mission named You Are Cordially Invited: RSVP.
After accepting the mission, start up the generator by the entrance to Tina's garage. Flesh-Stick will take the place of honour by the table. Approach and hit him with a melee attack (by default V). now head to the cave entrance, where you will have to stop three waves of Bandits from destroying the generator. After eliminating the last enemy, return to Tina to finish the mission.