Ah. I see.
Just couldn't figure it out, since modern dictionaries typically include colloquial meanings in a pretty timely fashion.
In this case, "gay" has been in use as a negative for a very, very long time.
You got it, I hear it every day "dammit that's gay!" in my Dept. I wouldn't say a very long time as you say it's an old word, and still it wasn't a negative connotation in my book, it used to mean fun and bouncy or something originally then was used to describe theater drag folks, then blah, evolved.