The Literal Commandment
A woman shall not wear man's clothing, nor shall a man put on a woman's clothing; for whoever does these things is an abomination to the LORD your God. (Deuteronomy 22:5)
The literal commandment is that men should not put on (i.e. wear) women's clothing.
It is one of only about two dozen or so things that G-d calls an abomination.