Encourage a friend to send you a SMS on their cell phone/mobile. The thumb being the key finger used in texting a message.

When you eat dirt for the first time and leave your family to build a shack in the woods

The request for an anal thumbing.

To put your thumb in an unwanted place.

An expression (often used in unison with explicit hand motions) that expresses distase or dislike for something someone has just said/done.

You're basically just telling them to shove their thumb up your anus.
Similar to suck me.