first you could explain to him that anyone that makes a blanket statment like "X amount of sets is best for such and such" doesnt know shit and should be shot at sunrise for giving out such dickhead training advice!
then you could explain that mucle grows during rest not during training and that overdoing it especially at the beginner stage is a sure-fire prescription for ZERO results.
i feel that is probably the single biggest misconception among people working out. many think there is a direct relationship to the amount of time spent in the gym and their results.
(the other big misconception is that all people into weight training should sport 3% b/f all year long and look like Arnold did in his best Olympia condition, lol)
you could also explain that the body grows best as a unit, which is why doing only curls all day wont do shit for your bi's past a marginal point.
if he scoffs at this, ask him to point out anyone in the gym with huge arms, a shallow chest and no back.
another point that merits explanation to a beginner is the fact that the bi's are some of the smallest muscles of the body and do NOT need a ton of exercises to get 'em to respond. If he wants to use guys like Arnold, etc as a rebutal just point out that yes they did a lot of arm exercises but they also did a lot of exercises period and they never neglected the major muscle groups. And they took roids. and they were genetic freaks. and their beginner routines were much simpler, shorter and composed mostly compound free-weight movements.
lastly you could prod him by simply stating that he's afraid to train legs, back and chest because training them is seriously fucking hard work as opposed to a bunch of pussy arm exercises