IIN he said straight people can't wear rainbows?

I have a rainbow towel and happen to also be straight and I wear it sometimes however just because I wear it doesn't mean I should stop wearing it because of a rainbow.

There's nothing wrong in a straight person wearing anything rainbow related.

The dude who you are describing sounds very snobbish aka condescending and has a huge ton of issues a head of him.

Not to mention people had every right to not be on his side and rather from what I'm assuming to be on the other person's side which you mention is your co-worker.