Oye, too many to choose from. Living on the West Coast, I've attended about a dozen games out here and the Bills won only once, the Rams game 2 seasons ago.
The Chargers game last year ended up a rout but it was a good atmosphere of Bills fans. I'd have to say the worst was vs the Niners in December of 2001 at Candlestick Park. Not only were the Bills never in a 35-0 game, it was cold, windy & rainy to make it extra miserable.