(at around 1h 7 mins) Right after Mahoney starts infiltrating the gang, and he's encountering Jones and the other cop, he tells Jones to kick the elder gentleman, then pulls him off all of a sudden. If you listen very closely, you actually hear him say "Jones", but obviously in the excitement, neither of the gang members notice and put 2+2 together.
(at around 49 mins) When there is a fight at the Blue Oyster Bar and Hooks go to find the address, Proctor says the address is 621 Cowan Avenue. When Mahoney and Hightower get there, the number on the door says 655.
(at around 47 mins) Around the middle of the movie when Officer Jones is fighting in the "Bruce Lee" scene, the clerk unloading the produce from the truck is seen sitting in an upright position when the camera is focused on him, but is seen in a slouching position when he is in the background of the fight scene.
(at around 46 mins) When Jones jumps up on the loading dock in the karate fight scene, he is wearing his gunbelt. In subsequent shots, he is not wearing the gunbelt. It is not shown on the dock where it would have been if he had removed it prior to the fight.
(at around 14 mins) At the beginning of the movie when Mauser is addressing everyone at roll call, Officer Vinnie Schtulman is present sitting at one of the tables. Later the same day, after Mahoney shows up (he was getting a new uniform), he is sent to pick Vinnie up at home and Vinnie is just getting ready for work.
(at around 57 mins) In the Japanese restaurant scene, the teppanyaki chef greets Pete Lassard (Howard Hesseman) by saying "ohayo gosaimasu, ohayo. Good evening." "Ohayo gosaimasu" is Japanese for "good morning." "Ohayo" is a less formal way to say the same thing.
(at around 28 mins) During the scene at Sweetchuck's store after the shootout, when Sweetchuck is trying to escape before being tackled by Hightower, the guy who tackles Sweetchuck is so obviously not Bubba Smith. Much shorter and lighter set, and considering Bubba Smith was an ex-NFL player.
(at around 34 mins) After Tackleberry tells Mahoney that he is in love with Kathleen Kirkland, he asks him to "keep this 10-35". 10-35 is the radio code for backup, while 10-36 is the code for confidential information.
(at around 40 mins) When Mauser is thrown outside nude in public, you can briefly see his white underwear. However, this is applicable only to the open-matte full-screen transfer for the home video release. When presented in its original aspect ratio, this detracting detail is not visible.