Charlie Brown does NOT say "aaaargh!", he says "Auuuughh!". There is no "r" in "Auuughhh!". The number of "u"'s and "g"'s and "h"'s is variable, but there is no "r".

Everyone else in the comic Peanuts says "Auuughhh!" too. (When under great stress.)

Lucy would give you a good piece of her mind, Bee-Dub, and she would go on about it at quite some length, possibly prompting you to go ARRRRRGH! at some point, but it would do you no good at all.