YANBU. It's pissy and unnecessary. If you think someone is a troll, flag their post to MNet Towers and don't feed it by posting on the thread. Calling "troll" does not make you fucking clever - frequently, you come across as an insufferable know-it-all and/or a dickhead.
I also hate those that track the OP's posting history and then decide to use that to attack them/diminish whatever they're saying. This too makes you come across as an insufferable know-it-all and/or a dickhead.
I also hate those who decide that an OP who appears to be posting for the first time must be a troll. Whoopee doo if you have managed to be on MNet and used the same nickname since your first day. There is nothing wrong with namechanging - and no, they should not need to justify their credentials to you by confirming their previous names (quite like the relative anonymity on MNet - if it didn't have that, most people would refuse to post anything, making for a rather boring and inuseful site) or referring to old threads to show that they have been using the site since time immemorial (the brown pouffe, penis-beaker, the fucking parrot with a dick the size of Mount Everest ... ok, totally made the last one up, but YSWIM!)
Just to make it clear, being an insufferable know-it-all and a dickhead are not mutually exclusive.