Do you have any girly physical/mental features?
For example: I have REALLY long eyelashes. Girls have even looked at me and asked "Oh my God, are you wearing mascara?" Yeah, they have a hard time believing that I can have longer eyelashes than them.
I also have a fairly pointed chin (it's more pointed than most guys' I know, anyway), and I'm pretty sure I'd have curves if I could lose some weight (not afraid to admit it, I'm a little chubby).
For mental features, I HAVE to be clean. Period. My room can be messy, but if I get a speck of mud on me, I freak. My fingernails also have to be perfect. And don't even get me started on bugs... I won't even let a ladybug land on me.