not lay a finger on (someone or something)
To not touch someone or something in even the slightest way that may cause harm or upset. Don't lay a finger on my son again, or I'll call the cops. I didn't lay a finger on your computer, I swear!
not lay a finger on someone
1. If someone has not laid a finger on another person, they have never hurt that person in any way. One of the men accused of attacking trucker Reginald Denny says he never laid a finger on him. Note: This expression is used in positive sentences for warning people. If you ever lay a finger on me again, I promise you faithfully I'll kill you. Diana's son now knows how to use the washing machine and refuses to let anyone else lay a finger on his rugby shirts and underwear.