C.A.
My youngest daughter did that for awhile. I had warned her that it is rude and she will get a time out if she did it again to her brother or sister, which is who she would only spit at when she was mad at them. But that did not work, so I told her that if she did it one more time I would wash her mouth out with soap. So of coarse she spit at her brother so I had to do as I said. I always follow through with what I say to my kids. I took a little drop of liquid soap on my finger and put it in her mouth just enough to give her a bad taste in her mouth. I know this sounds really drastic, but after a couple of times she stopped doing it. I would try other punichments first before I did this. I would also talk to the childs mom to see what she does to try and stop it.
Good Luck to your co-worker.
C. :)