Goofed batches of jokelate. See, when you're careful with boiled and minced poison joke, it actually makes a good flavor enhancer, but if you're not careful... well, let's just say it's minor to severe poison joke effects in one easy-to-snack package.

Bon Bon may be selling her failed batches to pranksters under the table. It's probably a small miracle Kyouko and Teddie haven't found out yet.