Kakarrot/Kakarotto

Probably one of the funniest, or weirdest, depending on how you look at it, things about the DragonBall series is that all of the characters (and even some attack names) are punned. With Goku, there's no exception.
Goku's saiya-jin name, Kakarrot, or Kakarotto, is a pun on the vegetable of carrots. All (full blooded) saiya-jins are punned after a certain vegetable. Bejiita (Vegeta), for example, is a pun of the word vegetables, with he being a prince and his father being the king of Planet Vegeta. Because of this, all of the saiya-jins are punned after other vegetables. Radditz, Goku's brother, for example, is a pun off of the vegetable radish, Brolly is a pun of the vegetable broccoli, and so on...
Even though Goku's "real" name may be Kakarrot however, no one addresses him by it, with the exception of Vegeta (and several other full blooded saiyajins such as Brolly, etc.) who always makes it a point to call him Kakarotto (Kakarrot).

To learn more about Goku's name, click here.