A goomba is actually a traitor who defected from the Mushroom Kingdom. However, "goomba" is "friend" in Italian. So... does that mean Mario has been killing friends all these years?!
No matter the definition, I call any mean people (or random people) goombas.
Where to find goombas: - Super Mario Bros. (every game but 2)
The Goomba Trophy (SSBM)