Buying a monkey
A situation in which someone who has recently come into a very large sum of money goes and buys weird, unusual, or taboo things, simply because they can. The phrase itself is derived from Michael Jackson, who bought a pet chimpanzee named Bubbles in the 80's following the success of his album Thriller.
Person 1: I've just fucking won 20 million in the lottery
Person 2: Man, that's a lot of money, what are you going to buy?
Person 1: I'm buying a monkey.
Person 2: Man, that's a lot of money, what are you going to buy?
Person 1: I'm buying a monkey.