This is brought up whenever a moral inconsistency in carnism is uncovered. E.g. Because of the environmental damage due to fishing, vegans will state that pescatarians are only pretending to care about the environment, and then "miss me with that gatekeeping" is a possible response. Or same with carnists only pretending to be "animal lovers".
Gatekeeping, according to the subreddit, is "when someone takes it upon themselves to decide who does or does not have access or rights to a community or identity." Examples of gatekeeping include scoffing "Let me know if you want a real beer, not Budweiser" or the classic "Oh you claim to like band X? Name 3 of their albums".
We're not trying to play some game where we are in some club and no one else is allowed in. Vegans are actually just trying to get you to hurt animals and people less. That's it. It's not about saying that you're faking being an animal lover. They're really just claiming your position is internally inconsistent. You're not practicing what you're preaching. The goal isn't like normal gatekeeping which is getting you to stop preaching (e.g. "stop calling that beer" or "stop saying you're a fan of that band"). The goal is to get you to start practicing.
It's not gatekeeping it's Gates Open Come On In/, just leave the animal abuse behind. Most vegans are extremely willing to talk about veganism and share recipes, food, and ideas.
Vegans are attacked for trying to convert people to veganism. So which is it? Are they trying to keep people out or bring people in
It doesn't really matter if you do or don't like certain labels, or you find vegans annoying, or you want to call these attacks "gatekeeping", or whatever. The important part is the human and animal suffering that carnism causes. Everything else is just white noise.