When it is late at night, and you can't call out to anyone, or no one is home and you take a dump and there is hardly any toliet paper left, and you try to use the last little bit and you get shit all over your fingers.

The result of the process of removing a condom after having anal intercourse with a female, or if you're into it, a male, partner.

this is what someone who fingers their own arsehole has.