I'm not finished.
I went to lunch with two co-workers. The waitress brought us glasses of waters (and straws) before our meal. The other two guys started getting their straws out of those little paper tubes they come in, but I just picked up my glass and took a sip. I said, "straight guys don't use straws" - not meaning it as anything more than a gentle bit of smack talk.
A bit later, I found out that one of the two was gay.
Was I trying to offend? No. Was I being offensive? Probably. Am I now more sensitive about it? Certainly - not because HR got on my case, but because I now know that I have a friend who is gay, and I can see the situation at least somewhat through his eyes.
Will I find some other way to screw up and be insensitive in the future? Probably - I'm not the most socially clued-in guy. But I'm not going to try to be offensive, and I'm learning to be more sensitive than I was.