Mine kinda happened unexpectedly. I got asked the question after a giant fight, and while I didn't say a straight 'Yes', I said it. I couldn't and still can't bring myself to say 'I'm gay'. If someone asked me, I'd say 'Yes', but I wouldn't say 'Yes I'm gay'. That 3 letter G-word makes me cringe every time I say it when its referring to me. I remember I didn't feel any relief at other people knowing because it didn't really change much, and I got severe depression for about 6 months after it. My parents were the first to know back in April '09 (I was 17 at the time), and my when I went to my doctor for an annual check-up I got the 'are you sexually active' question. I said yes, and she said 'with guys or girl' (a question they have to ask nowadays I guess), and I shocked myself and her by saying guys. She definitely wasn't expecting that answer, since I don't in any way, shape or form fit into the typical gay stereotype.
My brother, who started getting suspicious as to why I was leaving on weekends (I was going to see my boyfriend) took my phone and went through my text messages. He found some rather obvious text messages to my boyfriend and he was shocked. He couldn't believe that his macho, sports-playing, not in any way gay brother could actually be gay. He got angry and sent threatening texts to my boyfriend while we were out on a date, and that got me above the highest ager levels. I was going to go home and crack his skull open with my fists, but a very wise person convinced me not to do it. My brother and I (who have had a very rocky relationship for the last couple years for other reasons) stopped speaking completely after that, and we still haven't really talked to each other since. There was one incident over Christmas where he called me a 'Nelly Little Fag' and he readily caught my fist in his cheek and was knocked to the ground.
My parents accepted me for who I was, as I knew they would, and my brother was shocked at being blind-sighted and reacted with anger. I enjoy a good relationship with my parents, and enjoy (yes, I enjoy it) a minimal to no relationship with my brother. Now that I am in college, we have essentially gone to nothing, related by mutual parents and thats about as deep as we consider our relationship: One of unfortunate coincidence, not family.