Instaman notes that Donald Luskin is threatening to sue Atrios over calling him a stalker, which was Paul Krugman's charge. Luskin does some valuable work dismantling Krugman's unhinged and fact-challenged rants, but he often gets himself too worked up, and this is just way over the line for a fairly simple internet spat. Den Beste has some thoughts on what real libel is here (and on why these are tough claims to win here), and I'll say that for a non-lawyer he's got a pretty good handle on the basics.