shark thumb 

Shark Thumb.
The sexual act of placing you little finger (pinky) inside your partners anus (butt), while keeping all other fingers tucked in except the thumb that will stand proud and looks like a shark fin just slightly cresting the bottom of your partners posterior (butt) as they lay on their front.

During foreplay Sam Shark Thumb'ed meredith last night, meredith giggled as she looked over her shoulder and saw the shark fin (Sam's thumb).

shark thumb by Samqwell December 30, 2019

thumb shark 

Dickhead brothers (most commonly found in groups of 3) that resemble living breathing thumbs with shark characteristics. This is a rare species of thumb sharks can most commonly be found living right on the coast of Southern California near Redondo Beach

Girl 1: Those three boys just ruined our movie night
Girl 2: What a bunch of thumb sharks

thumb shark by thumbsharkhater456 November 25, 2017

share thumbnail space 

V. 1. Refers to the deepening romantic involvement between 2 individuals when both of them start to appear together in the thumbnails of their Facebook profile pictures. While anyone can share your profile pic, it takes a special person to survive the cropping and be part of the extremely limited 130 x 110 pixels that is a thumbnail.

2. Can also refer to non-romantic relationships, i.e. BFFs, bromance, etc.

Friend 1: Are Vangie and Phil, like, together? Their Facebook relationship status still says "single".
Friend 2: Yeah, but check out their homepages - they already share thumbnail space. It's official alright!

share thumbnail space by Nicnoc November 5, 2010