Thumb Sitting 

The action of putting thumb into butt hole before sitting. America's favorite past time for when you are bored and no plans.

Jill: "What are you doing today?" Jack: "Oh, just a whole lot of thumb sitting."

Thumb Sitting by UmmWhatchaSay March 3, 2018

sitting around with your thumb up your ass 

Doing nothing.

What have you been doing all day? Sitting around with your thumb up your ass?

sitting around with your thumb up your ass by brando56894 November 20, 2013

Sitting On Your Thumbs 

A term meaning commonly used to mean overweight and lazy, as the act of sitting on one’s thumb implies that they aren’t doing any work and are “flattening” the finger with their weight.

John: “You have been doing nothing except sitting on your thumbs all day, that’s why none of the other employees like you and you’re clinically obese.”

Sitting On Your Thumbs by wordsmith113 July 20, 2021