Each day in June you'll get an entry showing you the first appearance of seemingly minor characters, phrases, objects or events that later became notable parts of comic book lore. Not major stuff like "the first appearance of Superman," but rather, "the first time someone said, 'Avengers Assemble!'" or "the first appearance of Batman's giant penny" or "the first appearance of Alfred Pennyworth" or "the first time Spider-Man's face was shown half-Spidey/half-Peter." Stuff like that. Here is an archive of what I've featured so far.
First in-story reference to "Cap's Kooky Quartet"
Amazingly enough, the dramatic change-up in the Avengers roster in Avengers #16 where Thor, Iron Man, Giant Man and the Wasp left the team and Captain America stayed on with three reformed supervillains (Hawkeye, Scarlet Witch and Quicksilver) was never referred to as "Cap's Kooky Quarter" in the comics when they were actually appearing together. I imagine that Stan Lee referred to them as such in letter pages or Bullpen Bulletins (I can't find out where, though, so if someone can find an issue where he did so, let me know!). In any event, the first time the term actually appeared in a story was in Avengers #151, when reported Sam Reuther was doing a special on the Avengers making a roster change...
First appearance of Uncle Scrooge's "first dime"
Commenter AS wrote in with this one awhile back.
It made its debut in September 1953's Four Color Comics #495 (or Uncle Scrooge #3, if you prefer). Its debut is interesting. Check it out...
Note its use in the story (the Beagle Boys are robbing Scrooge)...
Quite different than how it was later used._________________________________________________________________________________
First time Johnny Storm shouted "Flame on!"
In Fantastic Four #2, the FF take on the Skrulls and Johnny shouts his phrase for the first time!
Thanks to reader Sylvain for correcting me on this one._________________________________________________________________________________
Feel free to send in ideas for future debuts I should feature here to firstname.lastname@example.org!