IPS if a relevant comment that has content can be fit into one line that is fine, but if the one line holds nothing but an insult to a previous poster, has no relevance to the thread itself, and holds no content other than the insult, then it is inapropriate to post it. It is also agaisnt the terms of use of the site and is classified as trolling. An action that is not only likely but guranteed to get a member banned from the site. How you proceed at this point is your choice.