The absolute worst for me was a kit called the "Visible Woman". I bought her when Revell still had the moulds and I thought the anatomical nature of the kit would be a nice change of pace from my usual aircraft modeling. As I understand, an outfit called Skillcraft currently holds her moulds.
According to the instructions and a nifty little pamphlet in the box, the kit was designed with the help of surgeons and other medical experts.
None of the internal body parts fit together worth anything and the clear exterior "body" components wouldn't close around the internal stuff whe it was all together. I was doing the non-pregnant version so I dare not even think what the complications would be if I had tried it.
The only way I could get the "body" to fit around the insides was to cut sections out of it, superglue it together and then paint the "body" to hide the crazing.
Well, she was a total failure when I built her as Revell. When I saw her a few years later as Skillcraft I thought maybe my skill were up to her, guess again!
I've heard Revell got the moulds from some other outfit who went belly up years back.
If there's any justice, those surgeons and medical experts who helped design the kit got their lisences revoked.
I like the idea of an anatomical kit, I just wish someone would do it with today's medical imaging gear. You know, MRI their insides and laser map their outsides and make sure the same individual was used for both sections of the model so the insides went in really nice like they should.