I can't pick up on a lesbian look. I have no gay-dar for lesbians, although I pick it up from guys a lot, whether they show any stereotypical "traits" or not. I'm actually pretty good at telling if an effeminate guy is straight or gay, or if a butch guy is straight or gay. Then again, I was a fag hag back in the day.
As for women, I can't pick up on it at all. There are some "stereotypical traits" but as with any stereotype they don't always show up on those they are about and they show up on some that they aren't about. I have straight friends who have that really short buzz haircut, dress in jeans and flannel shirts and don't wear makeup and have male oriented jobs, but are married with kids and straight as the day is long. (I had one gay friend who was married with kids before she finally came out when her son moved out of the house, so I threw that in that she's straight because some people are either in the closet or don't realize it until later in life)
As for the OP, your hairstyle and coloring reminds me a bit of Joan Jett, and people always said she was gay. However, I think Joan Jett is da bomb and gorgeous and I've always wanted to look like her. She's hot no matter what your orientation is, and I'd give my right arm to look like her! SHe really looked bad once that I've seen her, in that one episode of Highlander she was in. Her skin looked bad, and I think that might have been something that the makeup artists did for the character, because in the final scene when she showed up looking like the real Joan Jett, she looked great again. She aged well too.
So, I don't know why. Maybe you have characteristics that the stereotypical lesbian has and the people who say that to you are going on stereotypes. We all know those aren't true, but lots of people want to believe them. I don't want to offend, and don't mean this offensive at all, but I'll try and think of what some stereotypical traits are of lesbians that people may think you have.
Non feminine mannerisms. Walking or sitting like a guy or carrying yourself like a guy.
A certain way of speaking that I can't really describe. It's not "sounding like a guy" it's a type of enunciation of the words that's almost academic that you see a lot of lesbians in tv shows and stuff do.
Dressing casually in situations where other women dress less casually, or wearing man tailored clothing exclusively.
Having a traditionally male oriented job - construction, mechanic, fireman, police, etc
Those are the ones I can think of right now that some people tend to associate with being a lesbian. Of course, I think that if people have any question about what someone's sexuality is, and they are close friends enough with the person for it to be any of their business, they should just ask right out. It wouldn't offend me if someone were to ask me, and I've been asked out by lesbians before and I didn't get offended at all, I was flattered. I don't care if it's the same sex or not, I'm just happy that somebody somewhere thinks I'm attractive. I get no more offended by being asked out by women than I would by being asked out with a man that I'm not attracted to.
I think the next time someone asks if you are a lesbian, or assumes that you are, you should just say "No, why do you ask?" Tell them you won't get offended if they tell you, because some people think they are "dissing you" by pointing out something like that, when it's not dissing at all.
I've known lesbians who were in the process of an operation and who read as men, lesbians who aren't getting the surgery and still read as men, lesbians who fit the stereotypical butch, lesbians who fit the soccar mom, lesbians who fit the cheerleader, debutante, supermodel, and lesbians who fit all sorts of "types" of women. I've known straight women who fit all those types too, so it's not something that you can actually tell, unless you ask or they volunteer to tell you.
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I'm giving it another shot. We will see.
My forum is still there and everyone is welcome to come join as well. There is a private women only subforum there if anyone is interested. Also, there is no CAPTCHA.
The link to the forum is
http://www.rightplanet.proboards.com