Does the user appear to be bypassing attempts to block/ban him from the site/chat in question? If not, depending upon what you are looking at, one possible response is along the lines of: This is 2-way participation in an internet chat forum by 2 users who are at odds with one another. The quoted content may be ugly, but it does not appear to qualify as site or network abuse. Ch'Gans wrote:

Everything went well so far, until today. Someone, let's call this person/group "A", reported an abuse to Hetzner. A TOR User, "B", is spamming chat/forums with vociferous insults and disrespectful messages, I got a copy of few of them and the insults from B are as bad as the ideas defended by A, but I'm not here to judge anyone...