I used to have two gay cats, but the older one died a few weeks ago. They were always bathing each other and cuddling, it was adorable.
I have a silver Maine Coon cat named Shadowfax I am convinced is gay. He completely ignores female cats and has tried to have his way with some of the other males on more than one occasion.
My sister's bird is gay, and tries to mate with his bird buddy (who belongs to my grandma and isn't gay) whenever they see each other.
We had a dog a few years ago, who, after she was spayed, humped our other female dog. I agree though that it's a way for them to assert dominance. She sometimes humped pillows too so... But we found out that it was due to a hormonal imbalance after being spayed, and the behaviour soon stopped
