"Keying" a car is more than your run-of-the-mill vandalism. It's the same as any other serious offense. To be convicted, a prosecutor must prove that you have committed this type of vandalism. This means proof that you intended to cause physical damage to the vehicle, specifically to someone else's property.
Some states refer to this kind of crime as "criminal damage" or "malicious trespass" or "malicious mischief". In FL, it is considered criminal mischief, but it can become a felony charge if more than $1,000 of property was damaged.
You usually see this kind of case involving ex-relationships like boyfriends/girlfriends, or friends who are currently engaged in a feud. Sometimes it's something so petty that leads to vandalism, like keying someone's car.
When people get arrested for "keying", they are in shock. They refuse to believe that it is a serious or "real" offense. So, how much trouble can you get into for this "minor" offense? For example, let's just say you have to take care of the cost of the repair and repainting the whole car. That right there could run you a few thousand. Plus you still might end up doing some jail time. Was that worth it? I don't think so.
Remember that "criminal mischief" might not sound all that serious, but it's still considered a crime if you knowingly, willfully, and maliciously caused any damage to someone's property. Vandalism is crime that you will definitely need a criminal defense attorney for. Otherwise, this serious charge will become your legal nightmare.