Johnny Knoxville’s Bad Grandpa is hard to define in terms of genre. Part mockumentary, part narrative-driven film, it sees the Jackass star dressing up as 88-year-old Irving Zisman, who is forced to look after his grandson Billy (Jackson Nicoll) when his daughter goes to jail. Irving doesn’t want to be burdened with the tiny troublemaker, so the two take a road trip to deliver Billy to his deadbeat dad. Along the way, Irving and Billy get themselves into some hilarious and, quite literally, sticky situations with an unsuspecting public.

We sat down with Knoxville to find out how he made the transformation into a Bad Grandpa and pranking strangers.

Fandango: Where did the initial inspiration come from? Were you interested in doing a film with more of a narrative, or is it just that you are so recognizable you needed a new angle?

Johnny Knoxville: Paramount actually came to us eight years ago and said, "Hey, why don’t you do a whole movie with the bad grandpa character," and I didn’t see it then. In 2008, we decided if we were going to do that it would have to have a narrative. I thought the Paper Moon narrative worked for this.

Fandango: This film is hilarious and also has a surprising amount of heart.

Knoxville: I think you will be surprised by how much you’re invested in the relationship between the grandfather and the grandson. There is sweetness to it, and no one is really expecting that when they come to the movie.

Fandango: How long did it take you to put the old-man makeup on, and did anyone catch on to the fact that it wasn’t real?

Knoxville: Three hours every day. Five hours if I wore the chest and the back. Every now and then someone would recognize the Irving character, but we would just leave that location and go somewhere else and start pranking again.  

Fandango: In the credits I noticed you have an amazing actress in the film.

Knoxville: Oh, Catherine Keener? That’s one of those things… We got so much funny stuff with Catherine, and with Spike (Jonze) who played Gloria. We got so much great stuff with both of them, but it just didn’t work for the story. So in the end, we didn’t include it.

Fandango: In the credits, you show the people involved getting told it is all fake. It seemed like on the whole people didn’t mind being pranked. 

Knoxville: Sometimes they were a little upset. When I was doing the charades, one lady did not believe that it was fake. She kept trying to take Jackson’s picture. She thought he’d be on a milk carton, that I had kidnapped him.

Fandango: At times people were taking their own pictures and videos on their phones. Did anything ever leak to the Internet, where people thought it was real?

Knoxville:  I don’t think it did, because once we saw phones come out, after the bit... You know, we have so many people around to go and get releases, and they would get their phones and make them delete it. But that’s just a thing you have to deal with now. And it actually worked well for the bit with the drink machine.  

Fandango: Is it easier to make this kind of film these days, with all the technology available?  

Knoxville: Actually I would say it’s a little bit more difficult to make these days, because of all the other people’s technology, their own cameras and phones and things. But we still managed to pull it off. Despite our inadequacies.

Fandango: How did you get along with Jackson during filming?

Knoxville:  Oh he was constantly punching me in the zipper, intimidating me. Same with the director. When Jackson is around Jeff Tremaine, he’ll flinch every time Jackson moves. I do too.

Now go get your tickets!