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