Having a thick skin ought to save people from getting provoked when other people disagree with them, even when this is expressed a bit pointedly. It ought to be a safeguard against feeling obliged to throw out unbalanced abuse.

It doesn't always seem to work out like that though. Sometimes we come across the Rhinoceros Syndrome, where a very thick skin, which means that no criticism ever gets through, is combined with an ugly and very easily aroused temper.