most people just use their fingernails....just give it a good scrape then a little tap with a hammer. should work
Is that a joke? OP if you have an electric drill go to a hardware store and find a glass drill bit. They aren't that expensive maybe 5-10 bucks. Go very slowly while drilling the glass, pour water over the area every few seconds for added lubrication. If you go very slowly, you shouldn't crack any glass. However, I wouldn't recommend it as it's going to break eventually, your essentially weakening the glass.
Get a diamond drill bit or a diamond class cutter, You score the glass then lightly tap with a hammer and nail in the middle of the circle score you just made. It will break away clean. or should be pretty much clean if done correctly.
[ame="http://www.youtube.com/watch?v=kms2SMqRWto&annotation_id=annotation_793678&feature=iv"]YouTube- Broadcast Yourself.[/ame] heres how i did it
that shit had me bustin up. hahaha good one. but seriously, op said cut,,,not drill http://upload.wikimedia.org/wikipedia/commons/0/00/Glass_cutter.jpg this is what i have used, not the best for curved glass, but you score it with the wheel and then tap it with the ball to break it off, i had to wedge the glass in the littl notches and then break it off. or get a diamond/carbide drill tip to make a hole