The pee your cousin squirts in your mouth when your eating her pussy while she is choking and struggleing to get your cock out of her throat just before she blacks out
After any time you've been out and have had too much to drink ( coffe, booze, anythingliquid basically) and your bladder is so full that you go to the bathroom and need to go again immediately afterward.
Girl ( outside stall ) "Hurry up, there's a good song on and I want to go hear it."
Other girl ( peeing, in stall ) "I'm done, I just have to wipe.
Oh damn! I've gotta re-pee!"
Think of an absolutely awesome party abruptly and absolutely ruined by the arrival of your grandfather along with his comments about the insolent and hopeless youth. Well that's a royally grandpa-pee'd moment.
Well a grandpa-pee'd moment is pretty much obvious, you cannot miss it when it strikes down on you.