Unlike Swamp Ass where your entire ass is wet from sweat, Clammy Anus can be described as moist and sticky and only surrounding the rectum with some possible migration down to the taint. Where Swamp Ass occurs due to heat or heavy activity and smells mostly like BO, Clammy Anus is the result of seepage due to sickness or flatulence. The odor, while more subtle, is the combination of sick and poo. Not pleasant. Chaffing is less likely with Clammy Anus, but the sticky nature makes wiping ones ass more difficult as the paper is very likely to stick and tear along the affected area.
In general, you can imagine clams left out at room temperature for too long to describe the feel and smell of Clammy Anus.
After drinking too much last night and not feeling well today I was suffering from a classic case of Clammy Anus.