Clueless
Webmonkey
Ambient selfishness ("Are we gettin' paid for this?") combined with bloodthirsty enjoyment of violence ("... she *has* a name! I call her Vera..."). And let's be honest - if Mal weren't there and Jayne weren't scared of him? He'd probably have betrayed them more than once. Jayne is a great example of the principle that evil people can have friends too.