The worst I've ever heard was the english dub of the Gintama movie "shinyaku benizakura-hen"... no offence to whom it may concern but you could have really done a better job XD
I mean really??? take something as epic as the "crimson cherry blossom" and turn it into "The awesome cherry blossom"??? This is the reason why Gintama shouldn't be dubbed, its just gonna ruin the show ⌐.⌐