I have never owned a bad bike, I always insist on riding before buying. The worst that I have ridden were:
Water Buffalo.. Didn't run right, helped get me fired.
Sportster 1200... After a day riding my R100GS it felt like a total POS.
CR500 (85 heavily modded)... Truly Spooky. A bad crash in the process of happening.
The worst review I ever saw was for the Harley Night Train. The magazine called it the "Fright Train".