thumb buddy 

A texting friend on social media accessed from a smartphone, since you type mostly with our thumb in order to communicate.

Has my thumb buddy read my text yet?

thumb buddy by Storybored December 28, 2016

thumb buddy 

Someone who uses his or her thumb as a mutual part of the relationship. This can include constant thumbs up for a good job, or anal penetration.

"Dude, you have to do it, you're my thumb buddy!"

thumb buddy by dude man nice. May 14, 2009