I pretty much suspected it throughout my youth. My suspicions were confirmed in Jr High science class. The seating arrangement was tables and stools with no backs. I was seated behind a cheerleader (female) and spent a great deal of time throughout the year oblivious to what the teacher was saying.
I also frequently remained seated for a few minutes following the dismissal bell… umm… getting things organized.
The following year seated behind a male student resulted in much improved grades.
That one pretty girl in like 4th grade. She always wore pretty dresses as if she was going to a party or something. All the guys liked her. Or maybe it was my best frend’s mom at church around the same time. Compared to all the other conservative mom’s she was very spicy. I think she started my life-long fascination with breasts.
I knew I didn’t like men when the old dude (maybe 30 at the time, HA!) tried to grab my crotch back when I was maybe 13. Didn’t see that coming. Ick, ick, ick.
Sarah G******t. She was in my class in first and second grade and some other boys and I used to find excuses to do school things with her. I even remember being jealous if she would do a math project, or whatever, with another boy instead of me.
In the summer between second and third grade her family moved to Texas and for a couple years I would have dreams of going to Texas to try and find her.
There was this beautiful, tall, dark-haired girl 4 years older than me in school when I was about 7. Definitely made it clear to me that I liked girls.
ETA: and the above mentioned Playboys and similar magazines, but that was a year or two later.
I don’t know if I ever thought about it. It wasn’t something I knew in a conscious sense. At some point in my late teens, girls stopped being repulsive, so maybe then.
I was the girl in kindergarten that was chasing the boys to try to kiss them.
I had “boyfriends” in first and second grade. I had one in third grade as well, but he moved away. Ahhh, Ricky, I still think about you.* I don’t know whether I just didn’t click with anybody else, or if I finally realized that you had to have the guy’s agreement for him to be your boyfriend.
My first celebrity crush was on Captain Kirk. 
Not only did I go for men exclusively from an early age, I had an early marked preference for older men. Not for me the crushes on barely-pubescent teeny-boppers. I also had crushes on a couple of my father’s friends.
I can kind of understand where the original OP was coming from, after all, it sounds like a logical reaction to a bad experience. However, I have known enought hetero women who were sexually assaulted when they were young to believe that it is far more likely to make someone asexual, than to make them “switch teams”.
*It wouldn’t have worked out anyway - I was in the advanced reading group and he was in the remedial reading group.
I guess, being bisexual, I’m the “other alternative.”
The interest in men really hit after high school. I was very conservative in high school, so I didn’t date anybody. At all. But it was after I moved out on my own and was about 25-26 that I started thinking about being with a woman. My best friend at the time was interested as well, so we tried it. Oh, it was good. I loved it as much as I enjoyed being with a man.
I ended up in a hetero relationship, and am married to the man of my dreams. I still love women, and can really appreciate a beautiful lady: but I love him way too much to ever see anyone else.
I realized I liked boys when I was 3 and decided I was going to marry the 4-year-old boy next door. I remember getting vague crushes on various boys throughout elementary school, but the full-on boy-craziness didn’t hit me until about 5th grade. That was when I started liking a skinny, blue-eyed blond who pretty much acted like he didn’t know I existed, thus setting the tone for all my subsequent dealings with boys until college - boys either ignored me or rejected me mercilessly. It was also in middle school that I realized that a) I had sexual feelings for boys and b) it was not good to discuss this openly, for fear of being called names by other girls. It has taken me years to get over my “nice girls don’t get horny, let alone talk about it” hang-up. Like many women, I lost some of my inhibitions in college, but I still had many mental issues about sex that it’s taken years to overcome. Oddly enough, now that I am approaching middle age and no longer have a partner, I feel much healthier about my sexuality than I did when I was a (comparatively) hot college girl.
Realized I liked boys at about age 10 when I saw the picture of George Harrison on the liner noes for Wonderwall Music. It made me blush and gave me that ‘butterflies in my stomach’ feeling when I looked at it. I hid it where no one else could find it and would sneak looks at it.
Realized I liked girls when I was 12 or 13. I was into androgynous looking men at the time and my friends teased me that I was probably a little bit gay. But I was steadfast about my heterosexuality until a girl in my class got her hair layered and wore red lipstick to school. BAM! Same feeling of butterflies and blushing.
For the past year I’ve only been interested in men (and one in particular, who I’m now in a relationship with), so I’m currently identifying as heterosexual.
I always knew I liked dudes, but a few months ago a nice lady and I fooled around while my husband watched. I found it interesting and fun, but not hot. (Husband, however found it super hot) I guess that is when I realized I’m not really bi at all.
I’ve always been attracted to the ladies, but I guess I didn’t know I was nongay until I knew what gay was, right? That would be this one kid in middle school who was clearly a different kind of gay than the kind me and my friends called each other.
Thanks for this thread. I had thought of starting it myself.
How did I know for sure? When I made out with that dude and it was like making out with my brother. Bleargh ewww!! Oddly enough, I do go both ways just not romantically. Guys are fat and hairy and gross and I hope women never realize this about us. 
I’ve always liked boys. I’ve had several women try to convince me that I’m gay and I let a girl kiss me once to find I had no feelings - none, not even revulsion, just meh.
Not sure I really gave it much thought - you just continue doing what seems to work. Maybe something else would have worked so well, or not. Things just are the way they ended up.
Meh. We know, we’re just willing to accept it.
This, to a large extent. The first “I’d freakin hit that” moment I can remember was seeing Elizabeth Sladen on Dr. Who. Not the most typical schoolboy crush, but hey.
I remember chasing and kissing girls on the playground in kindergarten or first grade. Ginger and Agent 99 made me feel kinda funny down there. Finding some Penthouse magazines when I was 11 or 12 I thought “Wow, between a girl’s legs with their legs spread is not what I expected but that’s some interesting stuff right there. And boobies, boobies are just great. Round asses, oh yeah.”
This. I’d wonder even why women would go for guys since, as EvilTOJ said, there’s less than nothing appealing about the naked male body but naked girls are the bee’s knees.
When I was six. I was much more interested in the magazines my babysitter brought over than what he had in mind. I managed to get folks to make him go away after a while, but I grew up loving the Playboys.