Origin: Battlefield:Bad Company 2.
1) An in-game act of using any vehicle, primarily a M1A2 or T90 Main Battle Tank, and killing an enemy and/or an objective from a distance at or greater than standard vision at the firing position.
2) A term for when one person seemingly, instantly steals the attention between two people, be it the interest of a boss or the interest of the opposite sex. On purpose, or unexpectedly.
I almost had the perfect girl. We had similar interests and made each other happy. But then, some rich guy saw us together and Tank-Sniped me by showing her his Porsche. She hasn't called or text me back since.