Dirty Grandpa co-stars Zac Efron and Robert De Niro have teamed up to shoot a hilarious new Funny or Die sketch vid!
In the footage, the former High School Musical star attempts to persuade the veteran actor to wish his girlfriend Sami Miro a happy birthday via his iPhone camera. De Niro plays a super-serious persona and refuses to sing Happy Birthday to Zac's girl, or even smile as he toasts her big day with balloons, streamers, and a party hat.
Growing tired of Zac's requests for a happier happy birthday message, De Niro finally snaps and tells the hunk, "With all due respect, the two of you can go f**k yourselves. Did you hear that Sami? The two of you can go and suck my d**k!'"
But Zac appears to be thrilled with the outburst, turning the iPhone camera on himself and beaming, "Oh my God, you better love that."
Here's another LOL video, this time with DeNiro giving Zac "acting lessons."