"What's seventeen inches and resting on my thigh"?

Take out a piece of clear tape, put it where they touched the screen, take it off and put it on a blank piece of paper, then write their name and the finger they used on the paper. If they ask say it's "for my records."

In my opinion comedy only works in situations like these if you're also a bit silly/comic in other situations. Otherwise it's obvious that you're just using it to try to diffuse the confrontation and it doesn't work.

True. I'm silly most of the time.

I don't think your favorite line will work if it's a female co-worker though !

Well, she's certainly not going to touch your screen again.

That is definitly one to remember. And it is actually good advice, making a joke out of it will make the other person feel less bad.

Unless they keep touching the screen. Then it could get awkward.

As long as your laptop doesn't increase in size, you should not worry

Just up the ante. Scream like a madman, do a rain dance. Silly scales.

Ok, if someone used your favorite line on me it would provoke an entire hand rubbing across the screen, but then I'm a bit of a real life troll. :-)

I don't think what you would have done would be trolling, it'd be making a pass at him.

See: rain dance.

Or if they're wearing glasses touch those with your greasy fingers. They'll get the hint.