Darn Tootin' Meaning

(chiefly US, countrified, idiomatic) Absolute, utter, complete, very.

Example: 1916, B. M. Bower, The Heritage of the Sioux, ch. 28:
  Pink . . . nodded assent. "You're durn tootin’ it's right!" he testified.
2009, Lana Sweeten-Shults, "Look out 2009, here I come," Times Record News (Wichita Falls, Texas), 5 Jan. (retrieved 24 Jan. 2009):
  I’ve decided that Wii Fit is darn tootin’ fun.