When one's urge for a bowel movement enters into a death match with one's anal sphincter, and the sphincter slowly starts to lose like in a good arm-wrestling bout, until the feces actually touches one's pajamas.
I couldn't find an F'in crap hole for like an hour and by the time I got close to one, I was already pokin' pajamas!
I gotta shit so bad I'm pokin pajamas.
I forgot to put a diaper on my 2 year old when I put him to bed, and when he woke up he was pokin' pajamas.