Simply put, there is no reason for this movie to exist. It tries to be funny, but is not. It tries to tell a heartwarming story, but it doesn't. It is a film in a niche genre of hidden camera movies and every part of it is inferior to Sasha Baron Cohen's "Borat" (2006) and "Bruno" (2009).
Johnny Knoxville is made to look like an old man. It is well done and probably the best part of the film. He goes on a cross country trip with his "grandson". The humor is generally of the gross out variety or the inappropriately foul mouthed child/elderly person. This type of humor cannot carry a film; it might work for a bit or a sketch, but not for an hour and a half. It tries to make situations funnier by showing real people's reactions. However, the people's reactions aren't that funny. At least in Bruno and "Borat" the way people react to the title characters also reflects some sort of societal message or commentary. There is nothing profound in any of the Bad Grandpa sketches. Also, one bit, the raunchy child's beauty pageant, is taken straight out of "Little Miss Sunshine" (2006). It was funny then, but not so much now. It isn't shocking, since it's been seen before.
Even though the crux of this genre is people's reactions to various situations, it is accompanied by some sort of overarching story. In Borat, it was Borat's desire to kidnap Pamela Anderson and take her as his wife: a ridiculous plot to a ridiculous character. In Bad Grandpa, however, the plot is more realistic. The grandpa has to take his grandson, who he isn't fond of, to his biological father, but the father is a low-life. But in the end, Johnny Knoxville's character decides to take care of the child. The relationship grows primarily through conversations between the two as they drive. However, these scenes are surrounded by scenes of the two pulling pranks on real people. This juxtaposition makes the scenes between just the two of them seem incredibly fake and not believable in the slightest.
tl;dr This movie is awful, not funny, and came out 7 years too late. Only watch it if you enjoy dick jokes and laugh at swear words.
Johnny Knoxville is made to look like an old man. It is well done and probably the best part of the film. He goes on a cross country trip with his "grandson". The humor is generally of the gross out variety or the inappropriately foul mouthed child/elderly person. This type of humor cannot carry a film; it might work for a bit or a sketch, but not for an hour and a half. It tries to make situations funnier by showing real people's reactions. However, the people's reactions aren't that funny. At least in Bruno and "Borat" the way people react to the title characters also reflects some sort of societal message or commentary. There is nothing profound in any of the Bad Grandpa sketches. Also, one bit, the raunchy child's beauty pageant, is taken straight out of "Little Miss Sunshine" (2006). It was funny then, but not so much now. It isn't shocking, since it's been seen before.
Even though the crux of this genre is people's reactions to various situations, it is accompanied by some sort of overarching story. In Borat, it was Borat's desire to kidnap Pamela Anderson and take her as his wife: a ridiculous plot to a ridiculous character. In Bad Grandpa, however, the plot is more realistic. The grandpa has to take his grandson, who he isn't fond of, to his biological father, but the father is a low-life. But in the end, Johnny Knoxville's character decides to take care of the child. The relationship grows primarily through conversations between the two as they drive. However, these scenes are surrounded by scenes of the two pulling pranks on real people. This juxtaposition makes the scenes between just the two of them seem incredibly fake and not believable in the slightest.
tl;dr This movie is awful, not funny, and came out 7 years too late. Only watch it if you enjoy dick jokes and laugh at swear words.