It is one of the most insidious flaws of JS that you can add together pi and "hello" it will become the string "3.14159265358979hello"; i would have preferred a crash to such a nutty result.

There was a real bug at work that stemmed from getting two css properties like "12px", dropping the "px", and adding them together. After it was finally figured out, that became the joke with that coder: Hey, what's "12" + "12" again? (The observation was that this HTML element would shoot way down the page at 1212px)