do you know where "no beta we die like x" comes from and how it is used?
The term "beta" in this context is short for "beta reader" - a person who reads a fic while it's still in the editing stage and helps the writer get it ready to post. Some betas check grammar. Some check canon compliance. Some are sensitivity readers. There are lots of things that betas can do.
So functionally, saying "no beta" means that the writer didn't get this checked by a second person before they posted it. It's a warning that there might be errors or typos etc. It's mostly used when an author has written something quickly and is posting without doing a lot of (or any) edits first.
As for where it comes from? It all started with a bumper sticker.
This image was an internet meme at one point, and it got meme'd on in the form of "no ___ we ___ like men"
Here on tumblr, one of the versions that got really popular was from now-deleted user @grec1a who created this version:
From there, it migrated to AO3 as the "no beta we die like men" tag, and very often the word men is replaced by the name of a character who dies in canon.
Impulse: I told myself I was going to…get Gem to teach me about Tumblr! Guess what I didn’t do? I was gonna have a—I was gonna have a sit down, hands on lesson from Gem…about how to use Tumblr. It was gonna be—a fun little—boomer moment. (Snickers) Y’all are saying no Tumblr. Man, according to—according to some of the Hermits, Tumblr has been a much chill—more chill place than uh, than Reddit. Oh no, you guys just don’t want us on Tumblr, because it’s your—it’s your secret place. That’s why. You don’t want us checking out your Tumblrs, that’s—that’s where you—(laughter)—I see. I see. (Quoting chat) “Scatter.”
i was playing scrabble and i had a B, U, R, G, E, and R and i thought “aha burger, one who burgs, but my mom will never accept that as a word” but then i remembered burger is actually a word