My worst kit was an ACE 4-40 mid-wing sport plane. It was originally a costruction article in Model Aviation, as was its bigger sibling, the 4-60. Ace then picked up the planes for production.

The lite-ply fuse sides and bottom were so badly warped that you couldn't get the fuse to assemble straight. I glued it up and took it back apart 3 times before I gave up - the parts did make good templets to scratch-build a fuse out of balsa. The worked out resonably well as the fuse planes for this kit were printed 1/2 size and there was no Kinkos with their nifty enlarging copier to make full size plans then. Once I got the plane together it was a nice gentle sport plane with a Saito 45 for power.