Most of the original Fallout's "dark humor" was added just to make co-creator Tim Cain laugh: "We made this game for each other. When it shipped, we were like, 'Well, I hope other people like it!'"

https://www.gamesradar.com/games/fallout/most-of-the-original-fallouts-dark-humor-was-added-just-to-make-co-creator-tim-cain-laugh-we-made-this-game-for-each-other-when-it-shipped-we-were-like-well-i-hope-other-people-like-it/