pissed into your cheerios
When somebody is in a really bad mood, somebody might have urinated into his bowl of cereal earlier.
Person 1: *rant*
Person 2: Hey, who pissed into your cheerios this morning?
Person 2: Hey, who pissed into your cheerios this morning?
piss in your cheerios
When somebody fucking ruins your day that was going well.
Hey man I don't mean to "piss in your Cheerios" but I saw your lady blowing some guy in the parking lot at bar close last night.
pissed in your cheerios
To give somebody bad news.
"Sorry to have pissed in your Cheerios, but that chick that just gave you a blowjob has an Adam's apple and a hard-on."