the classic "mad-dog."
from urban dictionary: To stare fixedly at someone in a hostile manner. Generally used to convey anger or disdain, can be a signal that a fight is about to happen.
usually it's because they are insecure with their climbing or they are too cool.
just this weekend I was heading down from forestland, passing a number of bouldering parties on my way out I said hello to everyone, asked how their day was, blah blah blah.
as I came around the big fin at barney's rubble I saw two dudes and just as I was about to say hello this dude mad-dog's me, HARD, and looks away. I sat there for a second looking at them but they wouldn't look at me. so i laughed at em and walked away.