1. When you are borrowing something or stealing something from someone and you tell them
2. When you grab something in a sneaky manner (used as "thief")
1. I'm thiefin you're computer, man
2. Did you just see Alena thief that chair?
: the act of taking something from another, whether it be the theft of time, items/possessions, and people in which one may be involved in any form of relationship with.
Chelsea stole my idea. She straight thievin!
How are you going to just take his girl like that? Straight thievin, you have no loyalty.
The President of the United States, during these benighted times as America slips from moral leadership of the Free World into kleptocratic collectivism. (Derived from the appellation "commander-in-chief", reserved the the leader of the nation.)
"There isn't one bum in the race worth voting for. All they want to be is 'Thief in Chief'. Every one of 'em is a lying crook hoping the taxpayers still have a coin to squeeze before the nation collapses into insolvency."