In Superman IV, during the scenes which take place in space, you will notice that Superman's cape flutters. Now if he is in space, where there is no atmosphere, then his cape should not be fluttering because there would be nothing out there to make it do so. This error occurs in some of the other Superman movies also.
You people that bring things like this up make me laugh. In case you haven't noticed, Superman doesn't really exist. The movie is a fantasy. Lots of things happen in movies(especially fantasies) that aren't really possible. Let me guess, you thought Christopher Reeve was really flying too right?
OK, first of all, this is a very valid slip-up. I am sure the person who submitted this did not really think that Superman could be flying in real life. In the Superman movies, many laws of physics are violated, BUT ONLY THE LAWS PERTAINING TO HIS POWERS. When Superman flies, it is done on purpose, when he uses his laser vision to weld something, it is done on purpose by the creators. When his cape flutters in an atmosphereless space, it was done because of negligence. So my friend, your arrogance has done nothing but made you look like an idiot, just how most arrogant people look.