The act of pissing between ones butt cheeks, creating the visual of the Grand Canyon.
“Tonight, Martha and I are going to go make the Grand Canyon

Sheila and I cant make the Grand Canyon because she’s too flat”
by Cakeman June 14, 2020
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After titfucking a busty girl, cum between her tits unexpectedly and let the cum flow down between her tits.
Her tits represent the scenery, and the flow of cum represent river Colorado.
The phrase Grand Canyoning is a verb.

Example:
-"...I heard you had a 'special night' last night.What did you do..."
-"...I Grand Canyoned on her.She was surprised but it was amazing..."
by DepressedRetarded May 31, 2017
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when you convince someone that they've done something or gone somewhere (like the grand canyon) by fabricating a memory of it by telling them things you've done that you've told them about before
an example of grand canyoning:

person 1: dude do you remember when we went on a trip to florida?
person 2: no i've never been to florida
p1: remember? the lady at that gas station said they didn't know what our state was (happened to p1, but not p2)
p2: oh yeahhhhhh!! i remember that now (was told that story by p1 years ago)
p1: see, we went to florida
p2: yea i remember
by cheese demon June 3, 2019
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