The slot machine the progressive jackpot is won on shows that 2 coins are needed to win the jackpot. Jack deposited only 1 coin.
After Joy plays the slot machine that Jack wins the $3 million on, her spin resulted in no win. Just before Jack puts in his quarter in for his winning spin, the camera shows that the result of Joy's spin was Jackpot Jackpot Seven which should have resulted in a big win for Joy.
When Joy goes to work the day after moving in with Jack she is wearing a blue dress. When her boss tells her one of the ladies will be promoted she is wearing the gray dress she had on in the opening scene. when she returns home she is in the blue dress again.
When Jack and Hater try to see who finishes the beer first Hater's is gone and Jack has a little left. When they show Jack's glass again it is almost full.
When Joy is disinfecting Jack's bed, the bedding is solid blue. When we last cut to her, the top sheet is red striped.
When Jack rolls a 7 at the craps table during the retreat, the dealer pays off a number of field bets. A 7 is a losing roll on a field bet.
Joy throws dice that are opaque. Opaque dice are never used in casinos.
The slot machine that pays out the 3 Million Dollars is a progressive slot machine. The viewer can see by the payout chart on the machine they are playing that one quarter with a max pay out hit would only pay 1000 quarters. It would take two quarters to hit the progressive jackpot of three million dollars.
The initial shot of the Las Vegas "strip" shown just after both sets of characters leave New York was printed optically reversed; the casinos are on the wrong sides of Las Vegas Boulevard S and the signs for Bellagio and MGM Grand and the on-building sign for Monte Carlo can all clearly be seen to be mirror-images.
When Joy shows the marriage counselor a video of Jack and his two friends fighting outside her apartment with her cell phone, you can clearly hear their voices, but in reality there was no way to record their voices from her window.
When Joy throws the lamp in the hotel room, you can see a mark on the wall from the previous takes of the lamp being thrown.
At the retreat you can clearly see the drummer not making contact with the snare drum. His brush is in mid-air.
During the "flashing" montage of Joy and Jack getting together in their hotel room after their drunken night in Vegas, there is one shot where they are lying in bed and a crew member is visible in front of them.
Vegas wedding chapel marriages aren't real legal marriages unless the parties go to the clerks office and apply for a marriage license prior to going to get married. Since the two were clearing out drinking and completely drunk before getting married there would have been no way they would have applied for a legal marriage before going to the chapel. Therefore they could not have ever legally been married at all.
Jack, Joy, Hater, and Tipper were all drunk enough not to remember what happened the previous night, yet they don't have hangovers.