I look intimidating?

They're scared you might crush their balls under your heels.

Which is f***ing awesome to behold, I love girls like that.

well
there was this girl in my school who was really pretty but she looked mean

so therefore I would refer to her as the intimidating girl

They could be referring to how attractive you are, OR, that you have a look to you that invokes fear in others. I've known girls who when I looked at them they kind of scared me. It made approaching them difficult. It's not your fault though, some people are just born with a more intimidating look.

I'm sure at some point in your life you've looked at a guy and thought, "He looks scary!" I think that way all the time with some of the super buff biker guys who live around me, though, most of them aren't that bad, hah.

If the guys are referring to how attractive you are, they mean you look so good, they feel self-conscious and become unsure if they deserve you, and that they might look weird around you.