The worst co worker I had is actually pretty recent. He joined a well integrated team on what was basically a legacy project. He sounded like a good developer and seemed to know his stuff but it took him ages to push out fixes/features. They were always massively over-engineered, poorly named, partially tested and what documentation he did write still managed to bitch about how poor the project was structured.

He spent most of his time bitching about the general shitty nature of the project (he wasn't wrong) and the lack of interest from other Devs.

He was so unpleasant in interpersonal communication that by the end no one would work with him.

In his last team meeting he basically said he was glad to be going and that we were all lazy, disinterested and shouldn't consider ourselves his peers. The equivalent of storming out of a party after setting the couch on fire and shitting in the sink.

We've since removed all his overcomplicated, not standard, unmaintainable code.