Expect huge amounts of derp and rage, punctuated by /tg/ extracting humor from it.
A /tg/ slang term, referencing a fan of a now-defunct edition of any given tabletop game who is bitterly and verbally opposed to even the slightest of changes made in subsequent editions. "Edition X was The Best!" is essentially their catchphrase.
Grognards are most associated with the roleplaying game fandom, and as such the term is most frequently used among fans of Dungeons & Dragons, though wargames like Warhammer and Warhammer 40000 definitely have their grognards as well.
The term is taken from a French word meaning "a veteran soldier", or more literally "grumbler", which was first used to refer to members of Napoleons' Old Guard. This characteristic of lamenting the "good old days" and scorning the newer and more original is quite relevant to /tg/, since editions continually come and go in various tabletop games. Hell, with some tabletop companies releasing new rulebooks and FAQ updates between editions, perpetual debate spirals over what was better when prepare plenty of fa/tg/uys to walk the long and lonely path of the grognard.