It which point you reject the PR and suggest them to maintain a fork themselves.

I'd say don't bother suggesting anything.

Not as a rule for all prs you want to reject, but any time it seems to be no-effort pure ai. Both to waste as little of your own time and effort as possible, but also to to help make this activity not rewarding.

I wouldn't worry about false positives and being unfair. This is self defense and also community defense. Anyone legit will manage to get your attention. You'd be filtering not on any specific detail or rule but on simply "care".

If a legit person fails to convince you that they are a human that cares, then that's just an unfortunate industrial accident. It's unfortunate but trying to do anything about it is worse.

Besides, any actual adult understands that if they can't prove their age right now, then they can't buy a drink right now, even though they normally have that right, and is never the one trying to cry about the travesty of justice at being denied. If I submit a pr that fails your ai sniff test, I get it and don't think you're abusing me. I can try harder and we can be friends later no problem at all.