I am not gay, and I have never witnessed any bullying per se towards my gay colleagues onboard our aircraft. However, being close friends with 2 gay guys (the 3 of us trained together 15 years ago) I must say I've heard quite a few stories about gay crew being upset for the way they were treated by other colleagues...
I have on some occasions heard jokes being made about gay people by straight guys - some may say it's banter but forget that those at the receiving end may not find it amusing though.