One who is grossly sneaky, and or irregularly efficient at anything "Cloak and dagger", also, one who is generally good with the ladies.
-see also: anyone named Sean, Brendan, Devlin, and Noah, as all people with these names are sneaky (and good with the ladies) by nature.
That Sean is a Sly Casanova.
Those guys, they're Sly Casanovas.
Man, I wish I was a Sly Casanova.