Charlie Brown is still something more of a smart aleck than a whipping boy here, but it is an early example of Patty and Violet teaming up against the kid. Later on he loses this ability to reflect feelings of inadequacy back upon assailants.
Look at Patty's satisfied arms-crossing in the first panel. Man, that's some serious smug. Also in the first panel, that's quite a lot of detail on the background there.