Continuity mistake: When the guys reach the end of their downhill run, they encounter Blain, who is irked by their "shenanigans," going so far as to shove Jacob to the ground. When he pushes Jacob the large two-way radio that is in his pocket falls and hits the ground in front of him. However, when the camera angle changes to show only Blain and Chaz, the radio is back in his pocket without him ever having to recover it from the ground.
Continuity mistake: When the guys are at the lodge in their room, and they're sitting around the table talking about the past, the glasses on the table keep moving around in each shot.
Revealing mistake: The can of "Chernobly" is supposed to be from Moscow, and the lettering on the can contains at least one Cyrillic letter. However, the name printed on the can is nonsensical, using random Latin and Cyrillic letters in an effort to look Russian, but the letters don't spell a word and means nothing in Russian.
Plot hole: Sure, they say you should never question time-travel logic in a comedy movie. But when the friends that decided to get in the hot tub at the end return to the present, their future has changed. However, Lou acts like he hasn't seen them since then. This obviously cannot be: if they weren't there up until the point they returned, they wouldn't have had any of the things they returned to. Sure, they changed the future through their actions, but they'd need to be there for the next 20 years in order to maintain those changes. And they couldn't have existed, and replaced their present selves when they returned, as their present selves wouldn't have gone to the Kodiak Club anyway, since Lou wouldn't have tried to kill himself, so their present selves wouldn't have gotten into the time machine in the first place. Deep.