February 6, 1954: You know the thing I like best in the world? CAUSTIC SODA

Read this strip at gocomics.com.

There is spite, and there is this.  There's something almost affectionate about holding an entire party specifically to focus on something a particular, pointedly-uninvited person likes, although it's rather a lot of trouble to go through.  I can't help but think that the result would be rather a slapdash affair.  Why would you do otherwise, when the "guest of honor" won't even be there?

March 3, 1953: Lucy and the sandwiches

This strip makes no sense if you don't remember Lucy's prior fussiness over cutting sandwiches. This indicates that Schulz feels confident enough in her personality that he can use the character as a symbol of it, just like Schroeder is a symbol of both the artist and musicians in general.

This is different from Snoopy being a symbol of, say, dogs, or Linus of babies, because that's obvious from immediate reading.

The only other example of what I'm talking about that springs to mind are Charlie Brown's tantrums when faced with another character's quirks. Violet's mud pies don't count because Schulz only uses that in a context where the reader is reminded of her mud pies.