I don't think anyone intelligent enough to compose something resembling a valid DMCA takedown notice would be stupid enough to fake it in that particular manner, when the law deliberately leaves much wider and safer gaps for a sender to abuse the takedown process.
How about if you don’t live in the US? A few million lawsuit is not going to get you extradited, but let’s say the dmca request was created in Russia.
Not even then. Copyright infringement is normally tried in the infringer's jurisdiction.
So got any links to such cases? Its 100% certain some kids have sent invalid DMCA notices over the years. It's basically a prank that doesn't get you into trouble, at this point.