Ambisinister

adj., from "ambi-" (both) and "sinister" (left-handed, in its original meaning)

1) Clumsy or inept with both hands (i.e., the opposite of ambidextrous, which literally means "both" + "right-handed"; note that ancient Rome enormously favoured right-handedness, as China has in modern times)

2) Skilled or able with both hands (used generally in protest against the term ambidextrous because it implies right-handedness is preferable or ideal - ergo, this term is most commonly used by left-handed people, and also by hipsters and English majors who want to show of their knowledge of etymology and generally feel superior; very few people who use the term "ambisinister" are technically ambidextrous)

See also ambisinistrous, which has the same meanings and the same roots (however, the adjective sinistrous has been almost universally replaced by sinister over the last several centuries).