Blackmail refers to a situation that arises when a person threatens another person with some form of punishment if they do not offer some form of concessions. Blackmail is usually the result of one person somehow obtaining embarassing information about another and threatening to disclose it unless some form of payment (money or favors) is offered. The term originates from the words "black" and "mail", which referred to the dark or threatening nature of the letters (mail) that were received detailing the threat. Although blackmail usually entails paying a price to obtain another person's silence about an embarassing situation, it need not involve an actual event before it can be conducted. The threat of embarassing someone for a contrived event can be enough to conduct blackmail effectively, provided the threat is believable.

noun: a horrible or funny embarrassing picture of a friend or someone that you know that you are able to use against them
verb: (to) blackmail; to take an embarrassing picture or to use an embarrassing picture against somebody.

Mail for black people.

To beat someone in any sort of athletic event

Blackmail is slang for the method of sending messages via spraypaint on walls that black people commonly employ due to the fact that they are all too poor to utilize the postal servive.