When the President is revealing the reverse engineered alien weapon to the UN, he turns it on and it destroys the UN representatives clothing. But several men still have cloth head gear on, from the middle east (a keffiyah) and far east (a turban), that was somehow not destroyed.
shareI'm not sure this is a mistake, really, more a deliberate costuming choice for comic effect.
I mean, if you're going to nitpick over it, that's very far from the only mistake in the scene. For one thing, the extras move around all over the place. The 'Japanese' and 'Egyptian' delegates switch places 3 times during the course of the scene. The actors playing the 'Greek' delegates at the start of the scene, in the left-hand corner, are to be found behind Argentinian flags in the right-hand corner at the end of the scene. For another, the supposedly 'naked' actors are all clearly wearing skin-colored underwear or bodysuits.
And there are other mistakes as well. I mean, even if you buy a laser that can destroy 'material' in the sense of people's clothing, but leave skin unharmed, how do you explain the curtains at the back of the room that are clearly undamaged by the laser? Or the paper that the extras use to cover themselves? Apparently, the laser doesn't damage leather, because all of the extras are still wearing shoes even when they're naked, but then what happened to the leather jacket of the female 'Dutch' delegate? etc, etc.
However, what's the point of thinking like this? It's a scene about a clothes-destroying laser. Reason and logic weren't invited to the table in the first place. What's really happening is best thought of as a comedy ladder, with the ambition being to reach the top rung. A roomful of people being disgusted at the sight of an old naked guy is funny. A roomful of people being disgusted at the sight of an old naked guy, and then being stripped naked themselves, is funnier. A naked man is funny. A naked man in a turban is funnier. And so on.