Apparently, queer was originally used by gay men about themselves

In a non-derogatory way.

I really thought it was a reclaimed slur myself!

(Of course, key word there is reclaimed. If people from a certain group use a certain term about themselves in a neutral or positive fashion, then it's not a slur in that context no matter what the history is. Obviously. I kinda feel like this ought to go without saying, but apparently we have to say it?)