Whilst at Flanagan's place after a drunken night, they are watching a live broadcast boxing match featuring George Foreman vs Ken Norton. Since the film was set in present day US (1988) and the boxing match took place in 1973.
When Brian Flanagan takes a picture of Doug Coughlin on his yacht, he is sitting with his legs crossed, later he puts one foot up on the couch. When Brian looks at the picture later, Doug's foot is up on the couch in the picture.
When Brian pours Jordan a beer in the Jamaican bar, he is also making a drink for another customer. You then see Jordan take her first drink, and yet there is only about an inch high of beer in her glass.
Coughlin is saying, "There are two kinds of people in this world," and Flanigan is setting his drink down on the bar. In the very next shot, when he continues, "the workers and the hustlers," Flanigan is holding the drink as if he never set it down. It's also in his other hand.
When Brian and Doug are singing Chantilly lace, Doug falls down a flight of stairs and there is clearly a large puddle of water to the right of where Doug lands. In the next shot when you see Doug get back up there is NO puddle.
Brian brings himself and Bonnie a glass of juice in their bedroom. She hands Brian some vitamins and he pops them into his mouth. When he sits down on the edge of the bed and goes to drink some juice but there is no juice on the edge or rim of the glass. There should be since he needed some to wash down the vitamins.
During the film, the length of Tom Cruise's hair changes in different scenes. For the most part, his character's hair is cut short & tight to the head, with no hair hanging off the back of his head. However in a few select scenes, we see his hair is longer on top, somewhat styled differently, and with hair now hanging off the back and onto his neck. These were most likely reshoots with Cruise at the time wearing his hairstyle for Rain Man.
A server needs a Cuba Libre prepared. Brian later says to her "You bitch! Why didn't you just tell me that it was a rum and Coke?!" The drink also contains lime juice. However, both his recipe book and/or the server may have been wrong.