[undecisive]

Sure.

So I discussed this situation generically, because the specific situation doesn't really matter given the question asked. And no, I said it was impolite - but I totally understand that impolite is a big step up from toxic.

The bigger issue is, and maybe this doesn't apply here, but creating a situation where there may be a legal copyright claim to be made simply gives the a-hole more leverage over you, which is exactly what you don't want, if even the mention of his username is triggering.

(I won't point out that you mentioned his username 10 times in your blog post!)

So weigh up the risk/reward. If he's done a DMCA, and you've batted it back, the next step is legal proceedings. A license is exactly that - a license, it never assigns ownership. If I remember correctly, AGPL3 has protections so that he cannot revoke the license on a whim - unless you break the AGPL3 license.

You will never own the copyright to that file, no matter how much you desperately want to, no matter how many times you change the file, no matter if you remove his name, no matter how much you feel like you've paid in dealing with him being a dick. If he can make a case that the file you have is not significantly different in nature to the one he wrote, he still owns that file.

Toxic people will be toxic, but never get into a pissing fight with a skunk.