You're dern tootin'!

(Yer) dern tootin'!

slang (You are) absolutely right. An even more colloquial variant of "(You're) darn tootin'!" A: "Are you coming to the barbecue today?" B: "Yer dern tootin'! I'll see you there." A: "I'm sorry. It was wrong of me to leap to that conclusion." B: "Dern tootin' it was! But thank you fer apologizin'."
See also: dern
Farlex Dictionary of Idioms.

You're dern tootin'!

Rur. You are absolutely right! (Never the full form tooting.) Tom: Are you really going to take up boxing? Bob: You're dern tootin'! Father: Do you really want to buy that droopy-looking puppy? Bill: You're dern tootin'!
See also: dern
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • toot
  • tootin
  • yer
  • (Yer) dern tootin'!
  • dern
  • yer one
  • yer wan
  • yer woman
  • yer man
  • gotcha