If I called you a Republican as an insult, you would not be offended one bit, but there would likely be a similar response, of "that's not even an insult, broskii"
"gay" only works as an insult if you aren't gay. Like saying "you throw like a girl" only works if you are a guy....but I think the inference is that if you like a flat chests you are probably into men...
A stupid adorable hamster
Also it's plenty effective, as evidenced by all the people here reacting to it.
Just look at all the people reacting to the image. It's obvious that people know it's using "gay" as an insult.
What happened to physics?