Most Helpful Girl
You have to work on your expression.
It's subconsciously, that you are allowing yourself to come off as mean and unfriendly.
Try waving, making eye contact, or smiling at a member of the opposite sex.
This will break down lots of walls for that guy if he is interested.
I wouldn't say that's every guys reason for no approaching you.
But it definitely, could be a majority of their reason.
Why would someone want to approach someone? that looks defensive.