I did have someone whose username I didn't recognize PM me once, here, saying they wanted to challenge me on some post of mine or another. I believe the user mentioned religion, maybe Christianity in particular. I thought that was a little rude.
I replied, but as I'd been away from Wrong Planet for a while, the person didn't remember what s/he wanted to argue about.
Anyway I would say that if you sent a PM telling someone that the post you're PM'ing about was something you wanted to argue about or call them out on, that might be a bit rude. But just to say hi I like your posts let's talk one-on-one, I don't think that's rude. Other people might think it's too forward though.
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Your neurodiverse (Aspie) score: 141 of 200
Your neurotypical (non-autistic) score: 71 of 200
You are very likely neurodiverse (Aspie)
Official diagnosis: Austism Spectrum Disorder Level One, without learning disability, without speech/language delay; Requiring Support