I nominate the 'Mona Lucy' one from 'Lucy Goes to Art Class'. It's not that Lucy didn't do a good job mimicking the DaVinci painting and it was funny seeing her recap those Italian gestures she did in her earlier guise but it just was unbelievable that both Viv and Robert Alda had to walk around and up close before they could tell that Lucy was not a two-dimensional print. It would have worked better had they just peeked inside for a moment at a angle into the darkened apartment. ..and then when Lucy thought she'd fooled them, they popped in again and Viv would zing her! So much for the 'taking the ordinary and logical world and making it zany' dictum.

I thought the one episode where Lucy got super strong. Totally stupid.

I agree about the "Mona Lucy" skit. That was pretty far-fecthed that they didn't notice until they got right up close.

Another candidate would be the whole plot of "Mooney the Monkey". I mean, it's not as bad an episode as everyone says it is, but the story was almost totally unbelievable.

Basically everything Lucy did was zany and wacky, sometimes bordering on unbelievable, but these are standouts...:)

I vote for Mooney The Monkey

The episode where she had super human strength because of her "adrenaline gland" getting stuck. That was not believable at all, but funny to see her break everything up in Mr. Mooney's office with her extra strength! Also vote for Mooney the Monkey as well.