type-writer

A kind of shirt (ususally an over-shirt) that with time will sag or move to one side, thus causing one to have to keep pulling it back to the other side like a type-writer. This happens most commonly with girls as some shirts will move to one side as it flows, but gets stuck on a boob.

Guy: Hey, you've got some type-writer action going on.
Girl: Ugh! I know, this shirt is so annoying, but cute!