To bleach someone is to videotape them drowning to death in a glass cage, soak their dead body in a bathtub of bleach (hence the name), and then proceed to lay the body on a table, and suspend ones self above the table via hooks in the skin on ones back. At this stage one would masturbate onto the dead body while watching the videotape of them drowning.
This term is based on the way Carl Rudolph Stargher kills his victims in the psychological thriller film "The Cell" released in 2000.
The term is most commonly used in a humourous context.
1. Stop talking about my sister or I'll bleach you, cunt!