Deliberate mistake: In the prom scene at the end, there is a shot of a couple dancing with his hand on her rear-end. A counselor comes over and hits the boy's hand to make him move it. He complies, they kiss, and he puts his hand back when the counselor leaves. The camera cuts away to a different shot, and then returns to an over-head wide shot of the crowd. Down in the lower left-hand corner you can see the exact scene with the couple and counselor being filmed.
Deliberate mistake: In the final battle where El Guapo's men are fighting the townspeople, look closely to see that they are really just fighting Lucky, Dusty, and Ned. When the towns people appear, their outfits are very different from the real Amigos.
Deliberate mistake: The explosion of the ship at the end of the film is actually another angle of the explosion of the house from a few seconds earlier. The craft's explosion is much too small for what is shown in the film.
Deliberate mistake: While recon platoon is marching in their modified pt uniform, Gunny has "Cojones" call a cadence. Meanwhile Sgt. Webster maintains control of his formation, but from the wrong side. No platoon leader ever marches their unit from the right side of the formation.
Deliberate mistake: When Shelly Long is pretending to play a skilled violinist, to achieve this, when we first see this, Shelly's bow is above the strings; hence, no noise.
Deliberate mistake: When Howard is being sucked out of his planet by the laser beam the couch ignites but he doesn't.