During the sales trip the two main characters stop at a gas station to get gas. during this stop Tommy bends the door back and after some struggle gets it to the normal door position. Before Richard gets back to the car however there is a shot of the door all dented up but in place. When Richard pulls the door off it falls to the ground and there isn't a single dent on it. (Also, is it me or does it seem a little ridiculous that someone that loves his car so much didn't notice the large dent down the edge of the door as he faced it while walking from the station to the car?)
The huge bruise on Tommy's face, from the board hitting him, disappears in less than a day.
Richard vacuums up moths - how many motels have vacuum cleaners in the rooms?
If Richard's hair gets blown off by the engine, how come it never was blown off in the convertible car?
When Tommy's "stepbrother", Paul, is shooting out the tyres he drops a cigar. When panned out there is no cigar on the ground.
You hear Richard unzip his pants when he sees the woman diving into the pool, but even before he goes to the window he is wearing boxers. Boxers are all buttoned, they don't have zippers.
Where does Richard get the board to hit Tommy in the face?
The hooks in the brake pad division (the one Tommy is fighting with) stop automatically when Tommy walks by. He turned them on, but he never turned them off.
When David Spade's character first pick up Chris Farley he tells him he, has just put a 440 with a 6-pack carburettor, but later when the hood flies off you can plainly see that it has a regular 2-barrel carburettor and air filter.
When Lowe pretends to be using the phone after screwing with the computer, the reciever is off the hook for about 15 seconds and sounds that weird signal when the phone has been off the hook for too long. It takes about 2 minutes to do that, not 15 seconds.