FAFO stands for "F*** Around, Find Out" (a profanity often implied or censored), which is a slang phrase used to warn that actions have consequences. It means if someone engages in risky or provocative behavior, they will eventually face the results of those actions. This phrase is used to caution or admonish and has gained popularity in social media, politics, and popular culture as a way to say "you will find out what happens if you take certain actions".