Saying “all of us were normal and (one was) a gay guy” was setting the gay guy apart and labeling him “abnormal.” I can understand the screaming. What would it sound like to you if you heard one of the gay guys describe his group of friends as, “all of us were normal, and (one was) a straight guy…”? Talking about sex at work is inappropriate, whatever the speaker’s orientation. You could ask your co-workers to change the topic or take their conversation elsewhere. It would be fair to accept that they would expect the same consideration from you.