People haven't really given apples to teachers, that I'm aware of, in the years since 1954, where as Charlie Brown remarks was already an outdated notion. And yet, we get this joke, the lore of teacher-apple-giving still lives. (My guess, which could easily be wrong, is that the custom arose as a way of helping to support teachers, who were traditionally spinsters.)
Oh, how I love this strip. It's awesome. I love it so much that, over on Metafilter, I've started using "phooey" as a general term of disdain, usually against people who are trolling or spouting incredibly stupid opinions. (Them: "I don't vote, and I don't see why anyone should!" Me: "Phooey to you. Phooey all over you.")
I think why I love this, more than how funny and yet satisfying it is to read "Phooey to you Charlie Brown," is that Schroeder says it twice. The first time we don't know why he's angry; the second time reminds us of his anger. It is perfectly constructed, it reads great, the sentence has a great rhythm, just, wow. This is one of my favorite strips to date.
This is either the beginning, or close to the beginning, of Lucy's obsession with bugs, which drives a good number of strips to come.
In case you hadn't noticed, Charlie Brown embarrasses easily.
A strip like this reminds us of how relatively recent casual sexism was. I'm not sure many comic characters could get away with Charlie Brown's rude summation, although to Schulz's credit it is rare that a male character gets away with declaring superiority to females without some form of rejection, refutation or comeuppance. Calvin might declare how much better boys are than girls, but he certainly wouldn't be allowed to get away with it.
The animated adaptions of Peanuts, in addition to not showing adults, also replaced speech with muted trumpet noises. I think the later days of the comic tried to get away with not printing adult words, but in the early days at least Schulz was not above the occasional adult speech balloon.