What does Butt Flag mean?

Butt Flag meaning in Urban Dictionary

That irritating little bit of wc paper that sticks towards butt and waves like a flag once you log off a public toilet you have actually lined with rest room paper to keep your ass clean and free of butt cooties. It's also created once you wipe your asshole with wc paper after which it unfurls within fingers; one end stays stuck to your asshole as the various other end dangles freely from your hand.