A Mickey Finn is an alcoholic beverage which has been adulterated with a substance which is designed to incapacitate the person who drinks it. In a classic Mickey Finn, the drink includes knockout drops such as chloral hydrate which render the consumer unconscious, although other variations involve the addition of drugs which cause someone to vomit or develop intestinal distress. In the modern era, the Mickey Finn is usually a drink which has been laced with a so-called “date rape drug,” a drug which makes someone pliable and forgetful.
People have been drugging each other's drinks for a variety of reasons for hundreds and possibly thousands of years, but the term “Mickey Finn” dates to the early 20th century. It appears to have originated in Chicago, a city which was famously rough in the late 1800s. Allegedly, a bartender by the name of Mickey Finn was in the habit of spiking the drinks of customers so that he could rob them. In 1903, he was put on trial and the bar was closed, and it seems strongly probable that the concept of the Mickey Finn is named for the bartender who popularized it.
Some people use the Mickey Finn with the intent of a practical joke; the victim's plight is supposed to be amusing to the victim or to the group in general. In these instances, temporary incapacitation without permanent harm is usually the goal, as the spiked drink is supposed to be all in good fun. However, victims of this type of practical joke often do not enjoy it, and sometimes bad drug reactions can occur, causing serious illness or permanent damage.
Classically, the Mickey Finn has been used to create an easy mark for robbery. Just as the bartender for whom the drink is named did in the late 1800s, a thief can slip someone a Mickey, as they say, and then help themselves to the victim's wallet and jewelry. Enterprising thieves may even take house and car keys for the purpose of a more extended crime spree.
A more sinister use of the Mickey Finn evolved in the late 20th century, when people started using drugs to spike drinks at clubs and parties for the purpose of committing rape. Typically, the perpetrators of such crimes are male, and they use drugs which are designed to confuse their victims so that the victim consents willingly at the time to sexual activity, or is unable to resist due to stupor, confusion, or physical incapacitation. One of the problems with such drugs is that they often cause memory lapses, which can make the victims unreliable as witnesses.