Refers literally to a man, but specifically to someone whose skills or physical stature make him especially intimidating. A badass
. Can be used metaphorically to refer to a woman, as long as she is a total badass at something.
There is a common misconception that this term refers to any male because it references the male organ, but the more important part of the term is "swingin'." That is, not just any man, but an especially potent or imposing man. Hence, a badass.
1) As in No Country for Old Men: "Call my room if anybody comes in--and by 'anybody' I mean any swingin' dick."
2) A: "Did you read that new Judith Butler article? She totally destabilizes the regime's reinscription of normative typologies."
B: "Yeah, she's a swingin' dick when it comes to critique. Also, stop talking like a d-bag."