In the office where I work, we have one of those Bunn coffee machines like in restaurants. It has three burners: the two in front are usually occupied by pots of Regular and Decaffeinated; the one in back is where the empty pot sits. You fill the empty one with water and pour it in the top to make a new pot of Regular or Decaf. Basic setup. It's understood that the pot with the orange handle is for Decaf and the brown handle is Regular. This is America. This is how it works.
So after lunch, I go to get some coffee, and there's Decaf but no Regular at the moment; someone is in the middle of making a fresh pot of Regular. Cool, I'll wait. He's fumbling around, trying to open the stupid coffee packets (which admittedly are a pain in the ass) and sees me standing there, so he points at the orange-handled pot and says something like "Here's some, this might take me a minute."
I tell him "No thanks, I'll wait for Regular." He looks all confused. "That's Decaf," I explain.
He still looks confused. "How can you tell?"
"You know, the orange handle." What, is this guy an idiot?
He says "Oh, is that how that works?"
I wanted to say "What the fuck planet are you from, dipshit?! The orange handle is Decaf; the brown handle is Regular. Everyone knows that!" Instead, I tried (probably unsuccessfully) to not adopt a condescending tone and said "Well, yeah" (but I still added "you moron" in my mind).
So... what, he thought one of the pots just happened to have a different colored handle, meanwhile we just guess as to which pot has Regular and which has Decaf, because there's no correlation between the two? Doesn't everyone know this?
And then it hit me: Oh shit! What if, in his obviously extreme ignorance, he's been putting Decaf in the brown-handled pot?!
I grabbed the pot out of his hand and smashed it across his face. A shard of glass must've severed an artery or something because there was a lot of blood and it just kept flowing, like a fountain, as I stood there triumphantly, laughing, secure in the knowledge that I'd rid the world (and more importantly, my office) of a horrible menace.
Okay, I might have made that last part up.