Lobster

1. One who is not a crab

2. A person who encourages another to obtain success rather than pull them down as a rejection of their own mediocrity

Antonyms: Crab, Hater, Doubter

Friend 1: This guy I know just started hitting the gym, I know he's gonna quit after a week
Friend 2: Don't be a such a crab- be a Lobster