The Feedback Forum on QTH.COM can give you some examples of how people have listed "problem" transactions, both good and bad.
Essentially, just tell us what happened. As Jack Webb would have put it, "just the facts, sir". Offhand, if you lay it out that "he posted this, I replied thus, then this happened, then that happened" it's not a personal attack. Now, if you decide to discuss his ancestry, or speculate on the marital status of his parents at the time of his conception... that might be a personal attack.
(JMHO as a grey haired beachcomber -- I am not a mod on the site, so you don't have to listen to me!)