I was at a customer's site recently, sat at someone's desktop computer, cleaning off a virus when they walked up to say hello.
I'd been having a lot of problems with the mouse not moving the cursor half the time, so I told the user that they ought to ask for a new mouse. "This one's crap" says I, "It's held together with sticky tape!".
"Oh, I'm used to it now" quoth the user, "and the tape is there to hold the coin on".
I flip the mouse over, and sure enough, there is a two pence piece taped to the bottom of the mouse, slightly lifting it and so spoiling the sensor's view.
"Why's that there?" I ask, already dreading the answer
"Oh, that's because I'm allergic to electro-magnetic radiation" says the user.
Rather than make a scene in the customer's office and start the user crying, I limited myself to "oh" and turned back and did my best to ignore how much the stupid was burning my brain.