If they were not illegal it would definitely be snakehead. I've never come across a meaner fish in my life. I remember when there were tanks FULL of them at the pet shops. Dirt cheap too. $10 for a 5" fish.
Next pick would be Dovii.
Even meaner would be a Fahaka or Mbu puffer. They are MEAN sob's and their teeth make the Dovii's look like a joke.