Scratch.

Scratch, scratch.

Scraaaaaaaaaaaaaatch!

Scratch, scratch, scratch, scratch, scraaaaaaaaaaaaaatch!!!!

Person: *scratches blackboard*

You: *-_-*

Person: *keeps scratching*

Screeeeeeeeeech!!!!

You: "......................" *glares*

Person: *stops mid-scratch* "Could you stop staring at me? I'm trying to scratch stuff here!"