Former Ufc fighter Anderson silva flunked a drug test for steroids and was skinny as a rail at the time. He was probably using to recover from breaking his leg.
If you want to get big to be intimidating, I would think martial arts would be in order, so that you can back it all up if ever needed. I saw two jacked mucle guys get in a fight at a strip club once and it was hilarious. They were slapping each other like girls. Size will bluff most people, but eventually someone will call that bluff.
Jacked up muscle guys usually end up being either huge pussies or have zero fighting skills.
Only one thing matters in fighting....training and experience. A small guy well trained in just about any decent martial art can rag doll / knockout guys much bigger than him.