I think I'm pretty good at insulting people, it just depends on how much you have hurt me (IRL). I have a limit to what is acceptable as an insult, ie I would never use something that I know would really hurt that person beyond repair, which may make me less vicious than a T type in my insults, but I can usually read enough about a person to use less yet still scathingly hurtful insults to do the job.
Like if a person was fat and very aware of it I would not use that as a weapon in an arguement, nor would I use past mistakes they may have made that bring them great pain in remembering, it's just too low for me to go.
(this will make no sense to some but I find it easier to just punch someone than use those insults)
Mind you certain people, and that's less than a handful, have actually made me so angry that I have gone that low, but they more than deserved it and their feelings were no longer a part of my concerns.
Online it's less personal therefore much easier to get into an insultfest, however I have noticed that I also won't sink below a line even then.