Errr, I did horrendously in physics but...
...even I know this isn't right.
From the New York Times:
“George Lucas ruined my life,” Ms. Fisher says, which doesn’t seem entirely fair. On the other hand, in a book full of weirdos, he emerges as possibly the strangest of all. He wouldn’t let Ms. Fisher wear a bra under her Princess Leia shift because, as he patiently explained to her, there is no underwear in space: according to Lucas-physics, if you were to wear a bra in a weightless environment, your bra would strangle you.