How exactly did Johnny Knoxville come up with the character of Irving Zisman for "Jackass Presents: Bad Grandpa .5?" Turns out, it wasn't that hard.

"Johnny said, 'I'm going to go do voice lessons and find a voice for this character,' and I think that lasted a day," Tony Gardner, the makeup effects designer for the movie revealed during the above exclusive clip from MTV's Mancation Sunday.

"He's very inconsistent with that Brooklyn accent," Jeff Tremaine, the film's director, added. "He falls back quickly into Johnny Knoxville."

And therein lies the secret! Yes, Zisman is an amazing character, but that's because Knoxville is an amazing character in his own right.

"Didn't put much thought into the accent!" Knoxville said, laughing.

You can catch way more "Bad Grandpa" when "Bad Grandpa .5" premieres on MTV, 10 p.m. ET on Sunday, June 15.