When you read a good AU fic for a different fandom and ask yourself "hey, how cool would a SSSS version of this be?! "—and then spend way too much time and effort trying to make it even though the last time you wrote any kind of coherent narrative was years ago.
Oooh, now I'm curious, what kind of AU?
Also: You know you're an SSSS addict when you spend way too much of your morning helping an obnoxious customer, but the whole time you can't stop thinking that her sweater looks like it could belong to someone in SSSS. (It was light blue, dark blue, and white, in a kind of zig-zag pattern that reminded me of Reynir's sweater.)