This has become our go-to party trick lately.
He learned it mostly on his own from youtube, because I still can't sing it through without getting stuck somewhere. He has a craze for maps and the USA and songs, so Fifty Nifty was an immediate favorite. I haven't been able to brainwash him into always saying California is the best (in the part of the song where you get to insert your favorite state) - he is a goof and always changes it up and Rhode Island won today (he knows he's being silly). I told him we would get to move the the USA one day and he was all, WOW, REALLY?! As if I told him we'd live at Disneyland one day or something.