Absolutely not! If you feel that this is important information that you would like to share (some people like others to be cognizant, others like to keep it private), then you should absolutely let people know "where you stand." It does not make you annoying, and if anything, shows a great deal of confidence in yourself and trust in your friends. Of course, this is up to you to make the decision to disclose such information, but don't let "being annoying" be a reason not to share your sexuality with others.
Absolutely not! Sexuality is a big part of who you are, and friends should accept that it's a part of your life. In my experience, my friends don't mind; it's just a natural part of our conversations when they turn to romance and sex!
"Every time someone steps up and says who they are the world becomes a better, more interesting place." Your sexuality is a part of who you are, but it doesn't define you and sharing a part of who you are with people does not make you annoying.