Rule of thumb if the guy curls more than you squat, leave him alone if hes hogging the squat rack. Sorry, I had to. But if his arms are bigger than his legs tell him hes using the squat rack the wrong way.

If he can't out-squat me, he can't handle me. Period

I didn't read the whole thread, but I like this article http://www.bodyrecomposition.com/muscle-gain/general-philosophies-of-muscle-mass-gain.html for mass gaining. Not to mention he links to his other, also awesome, articles.

Also, I agree with the guy that said you look, in your picture, like your arms are proportional to the rest of your body and not particularly lacking.