I recently was presented with this dialog box on my phone, which I nominate as "Worst Ever":
How many things are wrong with this? First of all, it's a double negative: "Are you sure you don't want to?" I had to read that twice.
User Interface guidelines going back 25 years, on the first page or two, suggest the obvious, that the button you click should continue the momentum of the choice that you are confirming. So:
Are you sure you want to delete the file "bad idea.rtf"?
I read the above dialog box and could not convince myself which button would mean "Yes, I am sure that I DON'T WANT to upgrade." Cancel sounds like it would cancel the upgrade, and Continue sounds like it would go ahead and upgrade me, when in fact the buttons mean the opposite: "Continue" means "stop, don't upgrade", and Cancel means "go back and choose again," which means I can change my mind and actually upgrade.
This is a needlessly confusing dialog box with the wrong buttons and a poorly-worded question. There are only three elements to the whole dialog: the question, and the two button titles -- and all three of them are terrible. Only a talking paper clip could have made it any worse.