The trick is to look incredibly unfriendly and busy. Sunglasses help too. Or at least they have in my experience.

Scary/crazy might work as well. Mutter loudly about killing them all as you hurry past. Or something. Also, when I was in high school, the hallways were always completely packed, so sometimes one of my friends would hold something aloft (no one ever looks to see what), and would shout "Tapeworms! Tapeworms! Coming through!" and the crowds would magically part before him.

Hmmm.