One explanation for the origin of the "Liar, liar pants on fire" rhyme involves the curiosity of a young country boy who stole a cigar from his daddy's smoke box and hid in the tool shed to secretly mimic his father. After the boy lit the cigar, his dad smelled the potent smoke and followed its trail over crunchy leaves to the tool shed.
When the lad heard his father's footsteps, he snuffed the burning cigar as best he could and stuffed it into his back pants pocket. The father opened the shed door and barked at his son to tell the truth about what he'd done. The youngster feigned innocence, saying he was looking for a hook to go fishing with a friend at a promising fishing spot nearby. The cigar in his pocket suddenly sparked into flame. The father spotted the smoke and yelled, "Liar, liar, pants on fire!" Then he swiftly turned the boy over his knee and whacked his behind, extinguishing the danger. Another possible origin for "Liar, liar pants on fire" is that it was derived from a poem written in 1810 by William Blake, titled "The Liar." The phrase is often used as a taunt on political blogs.