The lone "no" vote came from Louie Gohmert - Rep. Rep. from Texas.
The word is used U.S. Code, Title 1, Chapter 1 dealing with rules of construction. As in:
"The words "insane" and "insane person" and "lunatic" shall include every idiot, lunatic, insane person and person non compos mentis."
Gohmert is known for, among other things, his staunch opposition to Obama's health care law. He told The Hill after the vote that he's OK with using the word "lunatic" because, well, there are plenty of them running around Washington.