Hey Bill, look at the guy walking down the street with that T-shirt that says "I'm a girl"

Its hard since i have no idea what you look/dress like, but normally some makeup and more feminine clothing should solve that problem in a more...subtle way.

Cleavage. It's all you need ;)

I say that you should find a look that you like that's also feminine. Or just stop giving a **** what people think of you.

That's pretty straightforward. Good luck!

My hair is pretty short, I'm tall and flat chested, wear little to no make-up, no dresses or frills, no earrings or nail polish most of the time, am Asian (which matters in this case because it's unusual for Asian girls to be tall, and Asian males tend to look feminine enough to westerners) and people hardly ever mistake me for a guy. A slightly shorter or tighter shorts, a slightly more slender pair of pants, a more feminine shape, color or print on your t-shirt and sneakers... that's usually all it takes for people to realize you're a girl on sight. You don't need long hair or super girly hairstyles either. There's some subtle differences in female short and medium hairstyles that already give you away. Try to look up some styles online and you're sure to find one that makes you comfortable while looking feminine enough!

Hair too short? Small breasts? Follow up is needed...

Purchase them like Renee Richards. Yes, I'm that old

Boy George? Is that you?

Awww, I'm sorry OP. Things will get better with time, I promise! You never know how long a little make-up or jewelry can go :)

Very mature of you lashing out at someone else when you were the one that had the blonde moment. Honestly just learn to laugh at yourself, because you really did miss something extremely obvious.

My boyfriend likes to tell me that the more intelligent someone is, the less common sense they have :) sometimes, people dont understand the "simple" things, but it doesnt necessarily mean theyre not smart.