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An unfortunate happening that can occur some time after you take a dump where your ass begins to itch because your formerly clean sphincter has begun to "prairie dog out" a bit of crap that may not have successfully exited your intestines with your previous bowel movement. Typically this can result in one having to wipe again to both remove the new doo and relieve the itch brought on by it.
"My ass itches. I think I got the backbiter."
by Senator O'Biden January 22, 2012