Sufficiently bad PRs/comments/etc. are against the GitHub Terms of Service, look under section C (Acceptable Use), which links to https://docs.github.com/en/site-policy/acceptable-use-polici..., which then includes https://docs.github.com/en/site-policy/acceptable-use-polici..., on which you'll find multiple actions would describe posting AI slop (or things ancillary to it).

I wouldn't do this where it's not clear there was an issue, but for something like the really poor OCaml PR that was floating around, reporting the user to me seems like a logical step to reduce the flood.