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 te could have really done a better job XD
I mean really??? take something as epic as the "crimson ciliegia blossom" and turn it into "The awesome ciliegia blossom"??? This is the reason why Gintama shouldn't be dubbed, its just gonna ruin the mostra ⌐.⌐