Stupidity: When Cougar (and later, Maverick and Goose) report to Stinger's office at the beginning of the film, a photo of an F-5 in flight (or possibly a T-38) appears on the wall beside his desk. However, the F-5s that appear in this movie are standing in as MiGs. Of all the aircraft photos the set designer could have selected for this scene, it seems strange to use one of an "enemy" aircraft.
Stupidity: After the ammo is removed when the team are under the reactor coolers Vasquez is still on point, even though her machine gun doesn't have a flamethrower capability and her hands are too occupied to be able to use one. Should have been replaced by another team member with an 'active' weapon.
Stupidity: After the Defranco "assassination" Rollie learns he is a target and survives two attempts on his life. But instead of leaving town or finding somewhere else to hide for the night, he spends the night in his own apartment (even though he was well aware the killers knew where he lived). As a result, his girlfriend is killed and he barely escapes alive.
Stupidity: Scott spread his lie about the protagonist telling Dean, who tells Frank (without details, just that the guy is 'a good fighter'). So barely one person (acting rather childish for a supposed master) has any animosity towards the new fella. There are over two dozens people in the class (in a 'good guys' gym, not one of those evil moustache twirling villain dens) and yet everyone is happy and cheerful watching a black belt beat the snot out of a schoolboy redbelt, for no reason. Most people there are grown-ups and there are black belts; they should be horrified or at least VERY puzzled. (00:30:00)