A confirmation, made whimsical from swapping word-endings... The usage goes back at least as far as "Dirty Duck", a comic strip (graphic novel) written by
Bobby London in the 1970's, including the tag
line: "Posilutely, Weevil!" "Absotively, Mr. Duck!".
This, in turn, refers back to the theme song by the Gallagher and Shean vaudeville
act (big in the 1922 Zigfield Follies), each stanza ending in a punchline, and followed by Shean's query, "Absolutely, Mister Gallagher?" and Gallagher's reply, "Positively, Mister Shean!"
Blunting the
offense of doubting someone: "You'll be on time, then?
Absotively?", "
Oh, posilutely!" (Absotively Posilutely)