piss on (someone's) bonfire

piss on (someone's) bonfire

rude slang To really upset, irritate, or disappoint someone. Primarily heard in US. Sorry to piss on your bonfire, but you won't get any credits for the class unless you attend every single lecture. A: "Watch out, the boss is on a foul mood today." B: "Wow, I wonder who pissed on his bonfire?"
See also: on, piss