Rambo - while sitting in a helicopter blowing up water and mist over the already obscured windscreen, do you really need to close your eyes and play dead to fool the guy in the Hind 50 yards away, also blowing up water and mist. And would the RPG you got off through the window really instantly blow up the Hind?
How about the Atari-level weapons system displays of the F-16 in Iron Eagle?
Someone mentioned uneaten meals earlier. As a kid, my favorite food was fries. Always wanted fries. So the uneaten fries in Meatballs when Tripper goes to the bus station to stop Rudy from leaving always got me. Then a few years later, same with the "five orders of fries" that Tommy orders at the bowling alley in The Wild Life. Eat your dang fries.
Crocodile Dundee II - after Bob gets made taking pictures of Rico killing a dude, races back to the hotel, he somehow managed to put the film in a package for Sue. He packs in a panic, calls the DEA to get him out, then leaves a message for Sue about the package. Cartel guys are listening in the lobby. Now why didn't they just get the package? I'm sure there were not very many mailboxes between cartel HQ and tiny Columbian town, nor instant pickup. The dang package was probably right there in a drop box in the lobby.
My biggest one - Bull Durham. Crash gets ball from third after strikeout around the horn. New batter. Tells Nuke to hit the mascot. Nuke hits mascot - Ball 1. Crash and batter laugh, but Crash says not to dig in, he doesn't know where it is going. Batter bails out and misses pitch away, Strike 1. Crash throws to third for strikeout around the horn.
How does Jason Bourne manage to keep all of the cars, even a junker little French car or a taxi, running after getting absolutely smashed in wrecks, when even a fender-bender can disable a car if it punctures a fluid reservoir?