First, clear your throat of any flem that may have gathered. You want to make sure you're heard clearly. Then, take in a deep breath. Exhale. Take in another deepbreath. Then, at the top of your lungs, yell out, "NOU". At this point your friend will realize his stupidity and jump off cliff. Seriously? We can't help morons.
Gay is only offensive you want it to be offensive. It's only a word, no one is forcing you to think it means "derogatory word for 'homosexual'".