Reading through this thread i see people confusing the term "aggressive" with "dangerous"
Anyway...the most aggressive freshwater I've ever seen was my friends 5" manueli piranha in a 90g tank. It couldn't have ANY tank mates no matter how big or small. When it was time to clean the tank and gravel vac my friend would have to block him off because the Manueli would try to take his fingers off. It was insane.