Why Is "What The Heck" A Bad Word?

Answer 1

That's a phrase, not a word, and "heck" isn't a bad word in the US.

Answer 2

It isn't 'bad,' it's just a colloquialism. It comes from Northern English as a kind of profanely euphemistic alliteration of "hell". So you would only use the term on the street, or as reported speech in academic English.