Pop culture euphemism for;
1. Person(s) who kills a good mood, fun killer
, party pooper
2. Bringing a highly inappropriate item ill suited for the situation.
Based on this ridiculous account;
"In Fargo, N.D., a man, 33, reportedly stabbed another man, 37, during a threesome. The stabbing allegedly occurred when one of the men reportedly refused to switch positions during the sexual romp."
The expression bounces off the old adage Bringing a knife to a gunfight
"Ah shit, don't invite that guy! He'd bring a knife to a threesome
"His friend was known for bringing a knife to a threesome, so he wrote a list items they would need; better safe than sorry".
"Who brings a knife to a threesome!? Seriously!"