WARNING: BACK-TO-THE-FUTURE SPOILERS

The joke is in the title with a movie like “Hot Tub Time Machine.” You just cross your fingers that the jokes keep coming.

They don’t. Pretty quickly the necessity of the plot, such as it is, kicks in, and the jokes gradually disappear so we can move the story along towards its monumentally stupid resolution.

The beginning isn’t much better. We start with the usual schtick for cinematic down-on-their-luck schmoes:

1. Nick (Craig Robinson of “The Office”) is recognized at his customer-service job by a douchebag who remembers him from his glory days—fronting a band called “Chocolate Kiss”—and he’s embarrassed by it.
2. Adam (John Cusack) comes home to find his girlfriend has left him and taken half their shit.
3. Adam’s nephew, Jacob (Clark Duke), a fat 20-year-old, lives in his basement playing video games.
4. Lou (Rob Corddry), boozing it up, drives his sports car recklessly into his garage, plays air piano and air drums to bad ‘80s music, and, because he doesn’t turn off the car, nearly asphyxiates himself.

Everyone assumes it was a suicide attempt. That’s how these three friends (plus Jacob) reunite again. They were inseparable 20 years ago but they’ve since drifted apart, as friends drift apart, but to cheer up Lou they decide to go back to Kodiak Valley, a ski-resort town and one of the high points of their youth, where “Nobody gets carded and everybody gets laid.” In a way, this formula is similar to last year’s box-office hit, “The Hangover”: three friends plus a fat guy head to Nevada to party.

Unfortunately, K-Val is now run-down and full of “out of business” signs. Their room at the Silver Peaks Lodge smells like cats, their one-armed bellhop (Crispin Glover, the first—or, after Cusack, the second—’80 icon to appear), is surly, and the hot tub is empty and filled with an old, dead, smelly animal. “If Lou kills himself, can we go home?” Jacob asks plaintively, in one of the film’s better lines. Instead they sit around, play quarters, and bitch.

Until the hot tub comes magically to life. Why does it come magically to life? Who knows? Why does it become a time machine? Because a Russian soda drink, made with chemicals that are “probably fucking illegal in the United States,” spills on the control panel. Sure, why not? We know from the title that this is supposed to happen so it happens. And back to January 1986, and that glorious weekend in Kodiak Valley, they go.

Only gradually do they realize they’ve traveled back in time. They see legwarmers, big cellphones, geri curl, “Safety Dance,” “Miami Vice,” ALF, and Ronald Reagan making a speech. Reagan is saying, “My heart and my best intentions still tell me that’s true, but the facts and the evidence tell me it is not,” which is from his arms-for-hostages mea culpa, which is from March 1987, not January 1986. It’s the first of many, many anachronisms in the movie. There are so many they almost seem purposeful: a celebration of a “fuck it” society.

I had two thoughts when I first heard of the film’s concept: 1) Funny title, and 2) Who the hell wants to go back to the ‘80s? The movie agrees:

Lou: It’s the fuckin’ 80s, guys. Let’s do what we wanna do. Free love!
Jacob: That’s the ‘60s, dipshit.
Adam: No, we had, like, Reagan and AIDS. Let’s get the fuck out of here.

To us, and to each other, they still look like John Cusack, Rob Corddry, etc., but to everyone else, and in the mirror, they look like their 1986 selves. Lou has long, heavy-metal hair, Nick has a Kid (from Kid n’ Play) ‘do, Cusack is youthful, Jacob keeps shimmering into non-existence like Marty McFly in “Back to the Future.”

And just like Marty McFly in “Back to the Future,” they realize their presence in the past could change the future, which is their present, so they decide to, in essence, walk in their own footsteps and do what they did 20 years ago. Which means Adam has to break up with his hot, bouncy girlfriend, Jenny (Lyndsy Fonseca), Lou has to get beat up by the ski patrol, Nick has to go onstage and sing.

Except Marty McFly had a reason for not changing the future: otherwise he might not exist. Ditto Jacob here. But Adam, Lou and Nick? Their lives suck in 2010. They have a chance to do what most of us would love to do: relive their young adulthood with an idea of what’s coming. Example: it’s January 1986? In two months, Microsoft goes public. I’ll take ten thousand shares, please.

Things have begun changing anyway. Jenny breaks up with Adam rather than vice-versa, Adam meets a quirky girl from Spin magazine and begins a very 1980s, very Cusack-esque relationship with her, and the Denver Broncos lose a big game it was supposed to win.

The film has moments. At one point, Nick, who is so whipped he can barely “cheat” on his wife in his 1986 incarnation, tells Adam why he clings to her so much: “I don’t have my music. I barely have friends. Without Cathy, I’m nothing.” This is a frank and deep (and adult) admission for a comedy but the movie doesn’t do much with it. Instead it pushes the usual envelopes (Lou loses a bet and has to give Nick a blowjob—but he passes out first) or gives us scenes cadged from other, better movies (Nick wows a crowd with a Black-Eyed Peas song the way Marty McFly wowed his crowd with a Chuck Berry song). There’s a fight, a chase, and a kind of mystical repairman (Chevy Chase) who helps them, in the end, get back to the future. Except Lou. “ I really was trying to kill myself” in that garage, Lou tells Adam. So he decides to relive his life and make it better.

This would be an interesting twist if it weren’t so icky—if Lou weren’t so icky. Earlier in the film, Nick says of Lou, “Like the friend who’s the asshole? He’s our asshole.” He’s basically the Biff Tannen of the movie, and, like Biff Tannen in the “Back to the Future” sequel, he uses his knowledge of the future to create a crummy empire. Nick, Adam and Jacob swirl back to 2010, where Lou is rich. He started “Lougle” before “Google” (apparently it doesn’t require coding or anything, just a name) and fronted Motley Lou rather than Motley Cru (apparently it doesn’t require talent or anything, just a voice). Did Lou do anything good in the meantime? Prevent 9/11? Encourage George W. Bush to become Commissioner of Baseball in the early 1990s? And if he did start mucking with global events (Kuwait, Iraq, al Qaeda, Clinton, Lewinsky, etc.), at what point did the year he was living through a second time no longer resemble the year he lived through the first time?

“Back to the Future” was a good popcorn movie, and hugely popular in the summer of 1985, but it did leave us with the uncomfortable thought of what happened to the other Marty. In 1955, Marty helps his future dad grow a pair and that changes everything, and thus, when he returns to 1985, his father’s richer, Biff works for his family rather than vice-versa, and his siblings aren’t losers. Marty grew up in Family A but this is now Family B, and...he doesn’t know them. He doesn’t know anything he and his family did for the first 18 years of his life. More, he, Marty A, has now replaced Marty B, the kid who did do all those things with his family. So what happened to Marty B? Replaced? Erased? Out of existence?

Same thing here. These guys go back to 2010 and Nick is a former rap star and current record executive. Adam, instead of coming home to a house without a wife, comes home to a mansion with a wife—the Spin magazine girl. This is Life B rather than Life A. But Nick and Adam have the memories of Life A. So what happened to Nick B and Adam B? Replaced? Erased? Out of existence?

It’s a happy ending but should it be? Shouldn’t someone speak up? “Dude, I don’t know my wife, I don’t know my job. My memories for the last 20 years are now false. You stole my life!” Shouldn’t they be counting their friends to see who’s missing? Shouldn’t they be counting their children to see if they have them? Or lost them?

I know. I’m overthinking a shitty little movie. Would that I could rewind my two hours and live them over again with a good book.

Cusack and Duke wonder how they wound up in 1986...or in “Hot Tub Time Machine.”