Would you believe that "Doh!" (a la Homer Simpson) is now officially a word according to the Oxford English Dictionary. I've been known to use it occasionally (including this evening following the not-so-fun car crash I was in - for those wondering, everyone was okay), but now I'm going to have to start using it in more formal occasions. Hell, if the Oxford English Dictionary says it's a word, then it deserves to be used whenever possible.