This is a difficult problem to have to deal with.  Sometimes people who act like your coworker are insecure in some way themselves. Perhaps he considers it good natured ribbing and wants to be your friend but doesn't know how to approach you in the right way. Sometimes people act that way to get a reaction, and just being friendly in response will short circuit that, or even saying it doesn't bother you anymore and giving them a light ribbing yourself.  If the situation gets serious enough or escalates I'm afraid you will need to talk to your boss or the HR department, just do it in a professional way, emphasize that it is effecting your work.
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