MacGruber is a parody of the 1980s TV action show MacGuyver, in which a resourceful crimefighting guy foiled bad guys by defusing bombs and making weapons out of chewing gum and tomato soup cans, or something like that. I never actually watched MacGuyver, so I can't speak authoritatively. All I know about MacGuyver is what I gleaned from previous parodies of it, of which there are many - which makes MacGruber not only unfunny, but unoriginal and pointless as well.
How unfunny is it? Pretty dang unfunny. Things blow up, people blow up, grunty sex happens and F-bombs are dropped with enough frequency to suggest that the screenwriters decided to make hay while the network censors couldn't bleep them. I doubt that the network censors bleepin' care.
Ninety-two percent of the jokes in the movie are precisely this: Characters say the name of the movie's villain, which is Dieter von Cunth (Val Kilmer). The joke is that the H is almost silent. Isn't that bleepin' hilarious? Now imagine hearing that joke repeatedly for 90 minutes, and you'll know exactly how much you do or do not need to see MacGruber.
The other eight percent of the humor involves MacGruber (Will Forte) doing incredibly stupid things, usually more than once. Doing incredibly stupid things is not inherently funny, and I'm willing to declare that Forte is also not inherently funny - which is eight percent of the reason why MacGruber isn't funny. The other 92 percent is that saying "Cunth" over and over again isn't funny either.
The movie was written (more or less) by Forte, John Solomon and Jorma Taccone, who also directed. The plot is an effort to string together various clichés from '80s TV shows and action movies. Cunth steals a nuclear missile. MacGruber - an extremely decorated veteran of, apparently, all of the various branches of the armed forces, who has won every possible award and medal - is in retirement in Ecuador when colonel James Faith (Powers Boothe) convinces him to hunt down Cunth. Why? Because the villain killed MacGruber's wife on their wedding day.
MacGruber assembles a team composed of straitlaced lieutenant Dixon Piper (Ryan Phillippe) and Vicki St. Elmo (Kristen Wiig). Wiig is a very, very funny woman. She can be funny just blinking her eyes. She is, in fact, funny in MacGruber despite everything going on around her. She specializes in characters who know that they deserve better: quiet seethers who are surrounded by idiots.
Vicki, one suspects, knows that MacGruber is an idiot, but she just can't help herself; she loves him anyway. Maybe it's because she has feathered hair à la Farrah Fawcett circa the 1970s, while MacGruber has a 1980s-vintage mullet and sports a khaki vest and plaid shirt. That would make MacGruber very fashion-forward in Vicki's eyes.
Not that MacGruber warrants all that much consideration of why the characters do the things that they do. The reason is simple: It's in the script. Why it's in the script, however, I can't explain. Maybe someone thought that it was funny, but I rather doubt it.
Movies are expensive and time-consuming to make - even bad movies like MacGruber. Given limited money in the world, I can't fathom why anyone would bother throwing millions of dollars into a trashcan like this. I also don't know why anyone who didn't have a professional obligation to do so (someone such as myself, your faithful, long-suffering servant) would stay to the end.
In the interest of full disclosure, I must report that I heard a few halfhearted laughs from the audience with whom I saw the movie. During a particularly belabored and noisy sex scene, the girl behind me said, "He sounds like he's dying!" Actually, that was the sound of a movie dying.