Jayne is not a girl's name. Jayne will remind you of this fact by using his favourite gun. Best you remember...
Jayne is a straight -up mercenary: he's in it for the money, and the money's best on
Serenity. He likes guns, and things that you can shoot with guns. And let's not forget the money thing. He likes that a lot too.
Underneath the necessarily rough exterior, it's obvious that Jayne's cut-throat means are leading to a more self-less end. Also, he wears this hat:
Jayne: "Ten percent of nothing is...let me do the math here...nothing into nothing...carry the nothing..."