When Zac Efron [1] stopped by The Ellen DeGeneres Show on Wednesday to promote his new comedy Dirty Grandpa [2], things got real weird, real fast. The funny talk-show host got Zac to play a bad-behavior-themed game of Heads Up!, which made the actor do some supremely awkward twerking, give Ellen one hell of a lap dance, and make out with his fist. Watch the video above to see every hilarious moment, and then check out some of Zac's crazy-hot shirtless photos [3]!