a gym-scrub is a guy who goes to the gym religiously and convinces himself hes getting stronger by doing his reps less and less legit each time he does it. examples would be using your legs and throwing your back to do seated row, either bouncing the bar off of your chest or leaving an 8 inch gap when doing bench press and swaying back and forth while doing curls. the more exagerated the movement the more weight the individual can lift.
friend: why is that guy hella throwing the free weights around with his body?
ME: oh it makes him feel tough to do that with 50 pound dumbells cus hes a gym-scrub.