What are some words I could use to call someone who is not good at work? [closed]

I asked this question because the other question on workplace.se. I realized that "enemy" is not the right word to express my idea.

I was working with that person for about a year. He was bad at work and never followed the rules or standards. I didn't like him because of his performance, not because of his personality.

What are some words I could use to call him?

Solution 1:

You could label this person as being an incompetent colleague. Incompetent expresses the concept that an employee is unable, for whatever reason, to perform or carry out his or her duties at work to the best of their ability. It is a formal and common expression, easily understood by all.

People were shocked that he allowed some of his incompetent workers to stay on after a mistake.

^{Source: Dictionary.com}
If you prefer a more informal expression you could talk about your co-worker's shoddy work, or shoddy workmanship, which implies the employee took short-cuts, used inferior quality materials, and generally had a lax attitude concerning projects, tasks, meeting deadlines etc.

Solution 2:

I think unprofessional may describe the employee attitude you are referring to:

• not characteristic of or befitting a profession or one engaged in a profession; " unprofessional conduct"; "unprofessional repairs"

Also a shirker, ( as a more informal definition)

• a person who evades work, duty, responsibility, etc.

Source: http://www.thefreedictionary.com