The Lousiest Fitting, Most Poorly Molded kit you have ever Tried to build

Omni Yomni

The worst fitting kit I ever tangled with was a Vampire in 1/48-don't recall who made it. Glencoe, maybe? I bought it in a bag at a show, and it turned out to be a short fight because the thing came with two right side fuselage halves. Guess that qualifies as lousy fit. A shame, too. Had a really nice decal sheet. 

Glencoe was a company started by a modeler in Massachusetts that found and reissued a lot of ancient model kits made by companies long out of production back in the mid 90s.

These were kits that were going for a lot of money for partially built glue bombs on eBay. The decal sheets were by far the best parts of a lot of their kits. Very high quality.

Worst I've ever done...easy.  The revell 1:48 F4U Corsair.  Not only did nothing fit, it didnt look correct once completed.  Most of their "build a toy" kits were bad but this takes the cake.

i built it and gave it to my 5 year old to destroy.  Absolute trash