pee in (someone's) Corn Flakes(redirected from peeing in your cornflakes)
pee in (someone's) Corn Flakes
rude slang To really upset, irritate, or disappoint someone. Sorry to pee in your Corn Flakes, but you won't get any credits for the class unless you attend every single lecture. A: "Watch out, the boss is in a foul mood today." B: "Wow, I wonder who peed in his Corn Flakes?"