Capsaicin can irritate intestines just like it irritates every other mucus membrane. When that happens, they will often decide to speed up the substances trip, which leaves less time for water to be extracted. Other food will get dragged along with the expedited.

So you are left with a spicy, liquidy, morass of poor choices that burns the starfish as its last 'fuck you' on the way out.

Doesn't happen to everyone, but it does happen.