Don't touch my computer monitor when you need to point at things on the screen

Here's a real pet peeve of mine:  When someone needs to show you something on your computer, they feel compelled to touch the screen, leaving a greasy smudge.  Then, once you notice the smudge, you can't see past it - it will bother you until it is wiped away. 


You don't need to touch the screen.  Pointing in the general direction of what you want me to look at will suffice.  Don't worry, I'll figure out what you're referring to.  Just don't touch my screen.  


Or if you do, bring a cloth with you to wipe off your smudge before you leave.