Hot Tub Time Machine is an inverted comedy. You know how a lot of throw-away comedies are funny for about 80 minutes and then for the last 15 minutes or so they stop being funny and wrap up the story that you didn't care about? Well Hot Tub is funny for about 15 minutes, and then has about 80 minutes of boring plot, mostly of the annoying late third-act melodrama type, so most of the movie plays out something like this, "But we used to be such good friends, and now we never see each other anymore and sometimes it just makes me feel alone, you know?" Stuff like that might have been good in a movie with actual characters and development, but Hot Tub is admittedly just Back to the Future meets 80s John Cusack movies minus the charm.
Now, I am not above stupid comedy; in fact I laughed pretty hard when Rob Corddry projectile-vomits at a squirrel, which is about 15 minutes into the movie, but I don't think I laughed again until the car ride home. Okay, that's not exactly true; there is a subplot with a one-armed Crispen Glover that is pretty funny, but other than that it's a somber John Cusack lamenting lost love (embarrassing), Craig Robinson singing the Black-Eyed Peas in the 80s (very embarrassing), and Rob Corddry saying things like, "We could combine Twitter with Viagra... Twittagra!" (lacks the minimum amount of effort required to be embarrassing). That leaves Clark Duke with nothing to do, essentially playing Marty McFly without the charismatic personality, walking around making sure the other guys repeat the past so he can be born in the future. It's boring. I never thought I'd have to beg for a couple of dick and fart jokes from a movie called Hot Tub Time Machine, but there it is.
You might think that a half star is a little harsh for this movie, but it was just such an awful experience to watch it. I originally had it lined up for zero, but there are a few moments that are pretty good, too good to be in a zero-star film, like the low-brow scene referenced earlier, or simply the line, "It's called male bonding... have you even seen Wild Hogs?" No matter how much I hated anything else in the movie, that line is still funny. And maybe that's just it: on paper, it's not like this is a tough sell: a silly premise and four actors that are actually funny. And in practice it actually showed potential for a little while, but it just gradually grows worse and worse. It wasn't even entertaining to make fun of it. I noticed that even my posture grew more slumped as I grew more discouraged with what I was watching; by the end, I was somehow sitting on the small of my back and my body was turned away from the screen. If only my eyes and ears could have been.