I always start the sentence with... "I know this is weird, but..." It helps me get to the actual point of direct confrontation, but by blaming it on myself it helps absorb some of the awkward. Truly though, I hate it when people touch my laptop's screen!
Here are more examples of the same technique:
"This is totally my own OCD, but it drives me crazy if..."
"Just a sec, I have to apologize, but..."
"It's probably just me, but it kills me when..."
(Don't forget to smile and be apologetic, tone is key)