The Brief: A fan theory about a way for Ant-Man to defeat Thanos by shrinking down and then growing large has inspired a popular meme.

DEEP DIVE
Could Ant-Man save the Marvel universe from Thanos if he shrunk down real small, crawled into Thanos’s rectum, and then grew real big? A fan theory about this very question has been circulating online through memes.
Origin
Although this may be something that many people pondered privately, the concept blew up in April 2018 when Twitter user @filmgloss posted a theory that Ant-Man was absent from Infinity War because his ability to crawl up Thanos’s rectum and expand, thus killing him, would have taken away from the plot of the film.
marvel saw the post about how ant man could defeat thanos by crawling into his ass and instantly growing in size and that’s why they didn’t put him in the movie, send tweet
— c a t (@filmgloss) April 30, 2018
Paul Rudd addressed this in an interview, saying “I don’t know” if it would work and that “One thing we learned from Infinity War is that Thanos could take a lot of punishment.”
Resurgence
The Avengers Endgame trailer indicates that Ant-Man survived Thanos’s infinity stone purge. This reveal has made this meme popular once again with many variations joking about Thanos’s reaction to such an attack by Ant-Man.
Ant-Man And Thanos Memes
Be warned, some of these memes are a bit NSFW as they deal with a somewhat graphic premise.
An Eric Andre “Let Me In” Meme: