Welcome to the new guy, and just another FYI. Kut's post is an inside joke, if you stick around long enough you will eventually start to understand most of them. I have been here a couple of years and there are a few things I still don't understand. On the bright side, I have been here long enough to know that anything I don't understand yet isn't worth worrying about either.
To answer your question, the "Plinkster" title is simply a reflection of the fact that you are new. The more posts you make the quicker it changes to something else. I wouldn't worry about it, I doubt many people pay attention to it. Whatever posts you make, your opinion on any topic will be evaluated according to what you say, not by the tag under your username. Hope that helps.
As Rob63 notes the plinker title is just a reference to the post number and won't mean anything unless you insult a fanboy(or girl)s favorite weapon/caliber/accessory/politician, then it will be used as a bludgeon to discredit your opinion since you are only here for the 'Race to 50'.
Also as he said...don't worry about it. Or, become a site supporter and for a small fee you can name it what you like.