Since this is a WW1 list afterall, I will only mention that one.
The worst WW1 kit I have assembled to date is definitely the Tom-M 1/72nd Fokker D.VI. The Revell D.VII and Dr.I were obviously used to master this one, but the master maker did a half-baked job and didn't take some things all the way through. For example, the kit still had the Revell "fabric effect" we all love to hate...