First real encounter on this site

I've been back on this site for less than five hours, and there's already been a nasty side to it.

Somebody commented on one of my postings. A little comment without any real context - but one that made him sound like he had been abusive and unprofessional to some of his students.

I asked him to elaborate on his comment. He refused. I asked him to delete it. He demanded a justification. I told him his comment presented him in a light that he probably shouldn't be comfortable with. He refused to delete it.

I deleted it myself, in the end. But it's a bit unpleasant when this is my first real encounter on the site.