Stupid doesn’t have to be synonymous with bad.

A great example of something leveraging its stupidity to great effect is “Jackass.” The television series and its three accompanying films were full of hilarious physical stunts that were made even funnier by the cast’s enthusiasm for the incredibly stupid things they were doing. It was dumb reality television in its purest, most beautiful form.

But that was several years ago. That particular brand of vulgar, stupid humor was stretched as far as it could possibly go, and there’s nothing else to be added to it. That’s the problem at the core of “Bad Grandpa.” It’s tired and boring.

Fans of “Jackass” will immediately recognize the main character of this spin-off film. It’s basically a feature-length version of the Irving Zisman skits from the series and films, where Johnny Knoxville is made up to look like an old man. During the skits, he is followed by a hidden camera as he says and does incredibly vulgar things in public places.

In the movie, there’s a thin plotline about Zisman having to take his grandson, Billy, across the United States to be with his father, but it’s nothing more than an easy way to connect a series of new Irving Zisman skits together.

The ultimate downfall of “Bad Grandpa” is that it just isn’t funny. The Zisman skits in the old “Jackass” were generally pretty funny, but only for about five minutes at a time. A feature-length movie that is nothing but Johnny Knoxville acting like a dirty old man in public gets old quickly.

Another problem is that they just don’t do anything new with the character. Anyone who has seen the old “Jackass” skits remembers Zisman letting his grandson drink beer in public, walking around without his pants on and saying disgusting things in failed attempts to attract younger women. It was funny a decade ago, but it’s just stale now.

There just isn’t a whole lot to say about “Bad Grandpa.” It’s boring, unfunny and uninspired. It doesn’t push the envelope in any way, and it’s nothing fans of “Jackass” haven’t seen before. Put simply, it doesn’t need to exist.