Lick The Pants Off Meaning

(transitive, idiomatic) To thoroughly and decisively defeat someone, either in a physical fight or, figuratively, in a competition.

Example: 1916, B. M. Bower, The Heritage of the Sioux, ch. 9:
  "Dang you, Luck, if you wasn't such a little runt I'd come up there and jest about lick the pants off you!"