This will be in one of the mythical episodes, and its hard to fully explain with background on all the characters (which would make it long and boring maybe? dunno). Anyway, here's a short, maybe less funny version.
The #2 (who's super sensitive and lacks self confidence and compensate by being BIG BROTHER), cuts the cake at some office party. She uses a plastic knife. One of the vets (who's a fantastically blunt and foul-mouthed woman and overall good person) joking says something like "message to management: next time use a cake knife" (she frequently brings alchohol-loaded, anti-mormon cakes into the office and always brings a cake knife, which is apparently a thing).
The #2 gets super red, but calmly puts the cake back into the bag without a word, doesn't make eye contact with anyone, then silently dumps it in the trash before storming out and slamming her office door. Everyone looks around awkwardly, then the lady that bakes (still waving around a plastic knife) says "what the eff is going on with us? We’re stabbing each other…” and whatnot.
All the guys minus (minus one, who's awesome) exit the room. Then, the women (and that one guy) get the bag out of the trash and eat the cake.