Garrett Oliver said as much in the Brewmaster's Table, too. He mentions that you might get a fair number of "me too" pilsners, but finding a full-on bad beer is pretty unusual. My only experiences with bad German beers were related to questionably clean/cleared draft lines. We got the first beers of the day (a Ludwig Dunkel and Tegernsee Spezial) at the Hirschgarten a few years ago and both tasted pretty rough, yet I know both to be pretty good in every other instance. I can't imagine those Beck's Gold bottles in the train station vending machines are aging very well either. I think to find something full-on bad, you either have to hate a certain style or maybe you happened upon a bottle of Desperados, which I think is Dutch anyway.