I think Devil's Due and Where Silence Has Lease are contenders. lol 
Devil's Due is not that badly written, but it's too silly and goofy, and off the wall. Where Silence Has Lease is just plain weird! I don't really get it, the Enterprise discovers a hole in space, the "hole" experiments with the crew, reveals itself to be a sapient entity, and then wants to kill half the crew.

Devil's Due is not that badly written, but it's too silly and goofy, and off the wall. Where Silence Has Lease is just plain weird! I don't really get it, the Enterprise discovers a hole in space, the "hole" experiments with the crew, reveals itself to be a sapient entity, and then wants to kill half the crew.
