Ordo Grammaticus
Ordo Grammaticus is one of the most peculiar branch of The Inquisition, specializing specifically in being the Imperium's pissed off auto-correct. That being said, they don't only underline your mistakes with red; they also like to shove parchment with said mistakes in your mouth and make you write the whole thing all over, which is especially painful with that red pen of theirs stuck firmly in your butt (or eye if you've made REALLY stupid mistake). They justify this sadistic behavior by saying that they pursue the Emperor's own dream of bringing humanity to it's perfection. That being said, they are especially touchy about religious scriptures, official documents and decrees, etc. That however doesn't stop them from down right bulling lower-class pheasants, some of which don't even speak Gothic and are trying to contribute in their own way and...*giggle...*bursts into laughter...
OK, ok for real now
...if you actually took all of the above seriously, then read up a little more on the subject (although some of it was based on reality). In WH40k community people use the term Ordo Grammaticus for anyone who is essentially a grammar nazi. Although the latter term is more universal, Ordo Grammaticus is becoming more popular as a meme and as a fanfic trope that is starting to spawn new theories (more on that later).
Grammaticus Inquisitors
To identify one in real life you don't have to look further that your daily WH40k Facebook or Twitter page's comments and watch some poor bastard, who probably doesn't even speak English right or got into 40k just recently eat it by every single butthurt who is willing to jump on that brakeless Hatetrain. Of course some may refer as such to people who just edit pages like me, and to people like that I would like to tell to shut THEIR FUCKING HERESY-SPEWING WARP RIFTS THEY CALL THEIR MOUTHS BEFORE I TAKE THIS RED PEN AND...*INTERMISSION*
Theories
Fluff-wise there are several theories about things that The Ordo may have stuck their noses into and since not much is known about them and they deny most of that not much you're free to make up your own opinion, just make sure it stays your own if you know what's good for you.
- Ordo Grammaticus vs Commander Boreale
The most notable theory says that, as Commander Mr. Clean was becoming the Jar Jar Binks of Dawn of War, Ordo Grammaticus couldn't just watch as he desecrates the holy name of THE EMPERAH *BLAM* Emperor and spreads his foul manner of "speech" among his own Battle Brothers. The theory even goes as far as that they themselves sent Vance Motherfucking Stubbs to personally fuck his bald shit up and even that Cyrus was the one that provided him with the info to do so, being the sneaky bastard that he is. The theory even goes as far as saying that the loss of those 100 Baneblades was caused by a fucked up order on the Inquisition's part. Though this wasn't confirmed, there are rumors of seeing one of the Ordo's (now former) scribes strolling around his home town blindfolded with something that appeared to be about a dozen pens stuck in his eye sockets WHERE THE FUCK DID YOU HEAR THAT!?...ehm...I mean...Absolutely preposterous.