Getting caught "white-handed" is when someone is caught in the act of masturbating. They could be masturbating to porn, or they could just be having some fun with themselves on the toilet. White-handed refers to the cum that drips out of their penis and onto their hands if they don't clean it up right away.

The color of a guy's hands after he's done "pleasing himself."

When a man is caught post-masturbation, pre-cleanup.

The act of fucking a girl doggy style then right before ejaculating the man pulls out and spits on the girls back as he ejaculates into his hand. The girl then thinks that he is finished and turns her head around. As this happens the man takes his ejaculation in his hand and puts it on her head as he says, "Send out your Warg riders". Just as Saruman did in Lord of the Rings.

When one is caught in the act of masturbation during ejaculation, typically when parents walk in on teens.

Getting caught jerking it.

This occurs while getting head someone while they are on thier knees and you are standing. When you are about to cum, you take it out of thier mouth and bust all over your hand. (Palm side, preferably the right) Try to cover as much surface of the palm and fingers as you can. You then procede to walk behind them and grab the top of thier head in a "claw-like" manner, so that your fingers are on their forehead, similar to the mark the White Wizard Sauruman made on the helms of the Urukai in the Lord of the Rings.