When someone intentionally " throws you under the bus ". Its typically a fire service term when your coworker tries to make himself look better in the eyes of management. Its typically employed by probationary employees who lack the self consciousness neccesary to be successful.
Luke: Hey Chili! Did you see that Les didnt restock the restock cabinet?
Chili: No I didnt notice that... But I know you would never do such a thing. Your such a good employee..
A strategic move in racing to get past the car in front without actually overtaking it on track. The car behind will pit earlier, do a quick lap on fresh tyres and come out in front once the other car has pitted.
Commentator: 'Red Bull are pitting this lap, they might be trying to get the undercut on the Mercedes.'
Someone who tries to steal your business by offering the same service/product for lessmoney.
Javi Rox: Yo, I got these cheeseburgers! I sell them to you for a dollar!
Jay Nyce: I got those same cheesburgers for 50 cent!
Javi Rox: I hate that motherfuckin undercutter.