Hooroo is a distinctively Australian way of saying “goodbye”.
The "truly wondrous fantasmagorically splendiferously magickal word hooroo" (credited to someone's Uncle Wally) echoes two likely sources.
It's a bit of a joyous exclamation, as in "Hooroo! hooroo!
hooray!" (Darby O'Gill), and it's also something of an owl's hoot, as in "the proper hooroo, hooroo" (The Sword in the Stone).
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"For my part, I do believe I should go quite insane, were I to live in {a} Land where people wandered around screaming, 'HOOROO' at one- another". said Werewolfy"
Hotrod Johnson is when you are feeling more than good. The night of drankin, and whatever else might have been up your sleeve to amplify the fun, may be coming to an end but not if your in your prime. Once you get to this stage in the night you have the urge to let everyone know that you are Hotrod Johnson.
Guy: Dude how ya feeling?
Dude: I'm fucking Hotrod Johnson.
Guy: Perfect!