I find the term "crossdresser" offensive because it's only a one way term. It is used to describe a male wearing female clothing yet excludes a female wearing males clothing which is the very definition of the word.

Crossdresser
A person who dresses in clothes normally only associated with the opposite gender. A man who dresses in womens clothes is a male to female (MtF) crossdresser, a woman who dresses as a man is a female to male (FtM) crossdresser.

According to this, there are an awful lot of crossdressers out there yet only one side of that spectrum is ever called out on it.