Carl's achievement for stockpiling 500+ identical hats — awarded with open contempt and no reward whatsoever.
After a day that included a thousand-crawler rescue and the death of the game's number two, the only achievement Carl earns that isn't about the battle is this: Mentally Unstable Clothing Hoarder, for holding over five hundred of the exact same stackable clothing item in his inventory — the Homeward Bound hats he collected to save the crawlers stranded at The Abyss.
The system's commentary is characteristically abusive: what the hell is wrong with you, are you planning to open a thrift store, you might want to see a shrink — one that your group doesn't immediately kill. The reward line reads simply that they don't reward this sort of behaviour, because it's weird. Neither Carl nor Princess Donut receives anything else from the day but a handful of standard adventurer boxes.
A system notification with a joke where the reward should be.
The dungeon's response to an act of mass altruism: mockery and a shrink joke about Hekla's death.