Why did Robert De Niro stick his finger up Zac Efron's butt, you may ask? No, not to be weird or creepy, and no, not to check how firm the hot 27-year-old's glutes are... though that would be rather hilarious.
The duo is filming a movie called Dirty Grandpa and the awkward situation was part of a scene shot in Tybee Island, Georgia. De Niro plays a perverted Army general named Dick Kelly, and Efron plays his grandson. Interesting. He really is a "dirty" grandpa.
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The film also stars Julianna Hough, Aubrey Plaza and Dermot Mulroney, to name a few. It is set to be released in 2016.