It is the small amount of feces that is pushed out your anus when you stand up. This small amount of feces is not detectable by toilet paper when you are wipeing while sitting. This type of phenomenon typically happens when your shit is pastey.
After eating Thai food Dave typically had butt cheese that would make is ass itch like a Mu Fu during the day.
guys that do not mind sticking their fingers in each others ass and do not care who see's.
Bob and Dave are definitely butt buddies, you can tell by the brownish color on the tips of there fingers.