Whenever someone takes there finger and dampens it with saliva just to stick it up some body's nose.

A wet nilly also isn't limited to just using saliva. For example a person may also use some sort of spices, melted cheese, or really just whatever you want. In that case the word "wet" is replaced with any of what you are sticking up a persons nose.

"Cheese Nilly"
"Garlic Nilly"
"Ass Nilly"

A term used to reference cannabis/marijuana/weed.

Sticking either your wet finger or tongue into someone's nose surprisingly