I'd be your coworker, except I slap hands away. You touching my screen is just as inappropriate as you touching me. You did not ask nor did you receive permission to touch me or my screen. Just don't do it.
You are framing this almost as an assault. I think if someone slapped me while I was trying show them something at work I’d probably avoid helping that person again.
If you’re someone that can’t keep their hands to themself, then I probably won’t come to you for assistance. So we’re all in agreement.
How would you feel if I came up to you poking at your face? You may not have enough respect for other people’s property to think “it’s just a computer screen”, but the key point is it is just a computer screen that is NOT yours. Keep your hands to yourself, and we’ll get along famously. Put your hands on me and my stuff, and we’ll see how well you and HR get along
I don’t have greasy fingers and I don’t touch other peoples screens. It’s the idea that it’s now acceptable to slap peoples hands away rather than use language to request someone doesn’t do something you don’t like, that I take issue with.