I don't think a reasonable person would beleive that it was meant to be literal, so it's not libel or defamation.
However, one could assume this was not your first communication with said person and it's likely that previous communications were not exactly friendly. It could easily be construed as harassment and they could sue for an order of protection and possibly even damages if they could prove actual damages. Something along the lines of Intentional Infliction of Emotional Distress, but there is a high bar set by the courts to prove such things.
Also, you're a bottom of the pond scum sucking piece of shit.