Etymology: probably the '70s. Brought to current vernacular by the residents of Mod 30.
you: "sweet jamz dude."
your boss: "we'd like to promote you to executive vice president of corporate development."
you: "sweet jamz yo."
your ma: "hey, wanna hear sleigh bells' 'crown on the ground'?"
you: "hell yeah, ma...SWEET JAMZ!!"