Unless the person saying "_____ is gay" means that thing is either extraordinarily happy or is actually queer (like "that is a gay bar" about a bar that caters to a mostly homosexual crowd), this is one of the most common ways to sound both ignorant and horribly bigoted in so few words.

My younger brother has a tendency to do this. Such-and-such car is gay. His friend was acting stupid, therefore he was acting gay. Everything on the damn planet that he doesn't approve of is gay.

Every single time he uses this term, he comes across as a bigoted, ignorant asshole with no social graces.

Gay does not mean useless, stupid, boring, or any other negative adjective you can think of ... it means happy and, in American English slang, it is commonly used to represent a homosexual/non-heterosexual person. Period.

This may sound nit-picky, and god forbid I would force my gay philosophy on you, but there is some truth to the idea that rhetoric has power. Every time a person hears "gay" used as a derogatory adjective for an object or person in an out-of-context way, it desensitizes them to gay bashing, to hatred.

I don't think that's something we need to be any more desensitized to.