I try not to metagame, but I think I still do.
For example following a guy with a hugger on his face into surgery and shooting the shit out of it with the HoS when it burst
Now that's not entirely metagaming, if some forlorn creature bursts out of a man's chest then its safe to say you can shoot it. What I mean is people yelling out over the radio at the beginning of the round, "HOLY SHIT I SAW THE ALIUM QUEEN, XENO'S ARE ON STATION!" as opposed to "What the fuck was that? I just saw some weird black thing running around maintenance!". Or seeing a man get attacked by a facehugger and saying "HOLY FUCK GET IT OUT OF HIM, HE'S GOING TO BURST OUT A LARVA!"
This. Every time I play Aliens, I'm like, "Uh, guys, what the fuck was the alien thing?"
"What alien thing?"
"It was like, eight foot tall, black, long head. No eyes. I don't know, it just ran off into the darkness. Maybe they're attracted to electricity or something?"
Then, get facehugged (If I haven't seen someone else get facehugged), "Man, I'm fucking hungry as shit. My throat's a bit sore too. Gimme them cheese fries."
Facehugged (If I HAVE seen someone facehugged/bursted) "Oh god. Does this mean it's gonna happen to me to? Oh fuck man. Oh god. (Then, if I'm a 'brave' profession, like security or Captain or something) Listen, you gotta seal me in this locker. So this thing doesn't get out. Take my gun and my ID and stuff, and just go. Weld it shut, brother. (Or, I decide to go homicidal batshit beserker on the Aliens and rush them)"
And also, something I think should be okay, there should be relative levels of meta. Obviously Assistant #22526 isn't going to know dick about the Syndicate or Aliens or the Blob. But the Captain, the AI, the Head of Security, they probably have a fair idea of what the Syndicate is and their methods/tools. I'd say the Captain might have a fair idea about what the Aliens are, e.g. An explicitly hostile alien lifeform, no more, no less. Obviously, the Heads/Captain/AI wouldn't share this information lightly with the crew, to avoid panic, because of security clearances, and because some people might get the wrong ideas/decide to help the traitors/join the aliens/etc.
I've always worked under this assumption in my roleplaying. As a Security officer, I know enough to worry that 'Maybe that big black creature isn't so friendly...' or 'I don't think that guy should have a revolver/card that can magically open doors.'
As the Head of Security, I know enough to be like, 'Xenos. Hostile ones. We need to arm up and take them out stat.' or 'That man is a Syndicate agent. That's an E-mag card!'
As the Captain, I know enough to be like, 'Shit, xenomorphs. Acid spitting, they have a queen and some sort of strange reproduction that involves us humans.' or 'Syndicate traitor. He has an E-mag. He could have an uplink somewhere, or maybe a power sink. This bears serious investigation.'
The same goes for Changelings or Cultists or anything else. A normal Sec-officer might not know lings exist at all, but he sure as hell is going to taze your ass if you are looming over an unconscious person with a four foot long needle thing coming out of your face.
Then the HoS might know, 'Oh shit, shapeshifter. Anyone could be someone other than who they are now.'
The Captain might be able to identify them by species, 'Oh no, that's a Changeling. Highly dangerous shapeshifters, they can take on anyone's identity, they have highly dangerous stingers, and they're masters of disguise and cunning predators. They're fundamentally invulnerable unless you completely physically destroy their bodies.'
Stuff like that. Does this make sense to everyone else? In the world of SS13, there's probably varying levels of knowledge about all the stuff in the universe. I would assume the man they put in charge of a station (or woman.) and the Station AI would both a fairly complete knowledge of most threats to the station, the knowledge of such things might percolate down through the command structure. At the very bottom would be Janitors, Assistants, Librarians, and Clowns, who might be telling tall tales to each other about 'Giant invincible black monsters' or some such thing. And also, they might be directly contradicting the Captain/HoS/etc, trying to say they're being 'Overly extreme for wanting to incinerate that body!' or 'These creatures could be completely peaceful for all you kn-*Chestburst*' or 'Traitors? Criminal Syndicate? What the fuck? Who made a conspiracy theorist the Captain/HoS?'