shit in the punch bowl

to cross the line; an egregious faux pas; to say or do something so offensive or outrageous it brings everything to a grinding halt; like going to a party and shitting in the punch bowl.

"It was funny until Josh said that thing about his wife literally having sex with a rat."

"Yeah, he totally shit in the punch bowl on that one."

shit in the punch bowl by Doug Higbert January 5, 2009

A shit in the punchbowl 

When everyone is having a dandy time, and that one specific person ruins it for all.

Everyone was enjoying SallyAnne's party, untill Jim Bob took a shit in the punchbowl by knocking over the boombox.

A shit in the punchbowl by Coleycath98 July 17, 2011