For me, bad dubs are less about lost inside jokes and more about bad voice choices and writing. The worst that I've heard is Higurashi no Naku Koro Ni, but that's probably just because I'm so used to the sub. Some of the dub voices were like nails on a chalkboard. Although Revolutionary Girl Utena may be even worse because I've heard a few seconds of that in a review or something. I've never watched Japanese Sailor Moon, so it's the opposite for that (so used to the dub).
Speaking of inside jokes and such, it is really hard to translate those since some anime rely heavily on humor related to Japanese culture. That's why I love the English dubs for Crayon Shin-chan and Sgt. Frog. They just replace them with American humor...and it works.