First of all, you shouldn't apologize for telling people not to touch your screen. I would be curt about it when it happens: "Please don't touch the screen, th

First of all, you shouldn't apologize for telling people not to touch your screen. I would be curt about it when it happens: "Please don't touch the screen, thanks." And say it with a smile. That way it would almost be a disposable, passing remark like: "Watch your step.". Making a big production of it would be worse for both sides. You want to say something and just move on so the incident doesn't linger too long. In a way, you are trusting the person to get the point. If he/she doesn't get it then it's their fault, not yours. I can see how this would be difficult if it doesn't suit your personality or the one you project at the office.