Provided by yardwork (ex-DUer) on the subject:
1. I don't care about anybody else's sex life. (Implies that orientation is nothing more than sex acts.)
2. If that lifestyle makes you happy, I'm happy for you. ("Lifestyle" should never be used. An amazingly large number of people don't know that this word, especially combined with "choice," is always insulting and demeaning to GLBTQ. Further, the "If....makes you happy, then I'm happy" implies a negative. It implies that it's a choice to be gay, and that that "choice" is not very good. All around, not a helpful response, and one that is quite common in my experience.)
3. I fully support your choice. (On the surface, this sounds very supportive, but it's got several problems. One, that "choice" word. Second, it is not up to the speaker to support or not support the person coming out to them unless they are a very close relative like a parent or child. Otherwise, the implication that one's sexual orientation is something that an acquaintance can choose to support or not is offensive and demeaning. Would a person say, "I fully support you for being black." Not if they wanted to be perceived as sentient. If support really is a legitimate issue, a better phrase is "I fully support you. I love you and will stand by you always.")
4. You're the last person I would have expected to.... (Commonly heard by people coming out later in life. Often combined with those "lifestyle" and "choice" words. Sometimes honesty is not the best policy. Look, I know that I slept around with men in college and then was married to a man for twenty years. Obviously the news of my being lesbian is a surprise to everybody - including me. Thanks for sharing.)
5. Even though your choice is against my religion, I can be tolerant of other people's lifestyles. (Actually said to me by a psychiatrist during our first meeting. I dropped her)
6. I was once in the life. (WTF. Keep your self-loathing attitude away from me.)