gateway finger 

When a woman sticks her finger in her significant others ass and it potentially leads to other things going in there.
ex. Stacy kept trying to get that finger in there and i finally let her. Now i spend my free time shoving objects in my ass. That damn gateway finger is a bitch.

Stacy kept trying to put her finger in my ass while we were intimate. One day, in a moment of weakness she got it past my fortress. Now I spend most of my free time shoving objects in there. That damn gateway finger!!

gateway finger by The Pelz March 13, 2015