Doing an unasked-for favor for someone, and then using it to try and guilt them into doing something for you.
Sam: "So Bob shows up at my house randomly with some brown bananas and is like 'hey, you can use these to make banana bread,' and I'm like 'uh, ok, I don't really bake but thanks,' and then he invites himself in for an hour and asks to borrow $300."
Joe: "That's some prime favor sharking right there. But my mother in law is worse. She keeps buying usweird vases and knick-knacks we don't need and then calls us ungrateful if we don't spend hours on the phone with her saying thank you and talking about where we'll put them in the house. We keep asking her to stop but she won't.
The Sharingan is an ability that allows a ninja to copy, by mere sight, their opponents' techniques while gaining incredible reflexes and perceptive abilities.
I swear if I had the power of The Sharingan I would use it to destroy people like you