Def. 1: Used to describe something particularly easy, generally a task.
Def.2: Used to describe someone of the opposite sex, particularly in how easy it will be to pick that person up. A sure thing.
origin: beginner's little league game of the same name, where the degree of difficulty in hitting a baseball is reduced by placing it on a tee for the child to hit.
"I know the guy who runs that place, so getting our friends in should be teeball tonight."
Someone who exhibits lame tactics in competitive sports video games, usually against a human opponent. This could include but is not limited to running the same play over and over, using clock tactics, or anything else that isn't in the spirit of friends sitting down to waste time playing video games.
Player: "Man you're milking the clock in a video game? That's fucking twatballing, man"
Player: "Quit pressing pause in the middle of my play, you fucking twatballer"
Pajama casual is a term used when working from home and preparing for a video conference. All business above the waist and your pajama pants down below.