An annoying coworker can ruin an otherwise enjoyable job and push even the calmest person over the edge. The most notable traits of a bad coworker, in no particular order, are as follows. 

The talker. Overly chatty coworkers don't know that the rest of us are 1) busy, and 2) don't care. I'll be nice, but I don't need to know how messed up your life is. The eaters. Basically, this is the "microwaves tuna" guy, "the chews with his mouth open at his desk" guy. And lastly, the type of coworker we're all in danger of becoming, the "it's not my job" guy. 

So to those of you currently looking for a job, maybe rethink what you're getting yourself into.