That would be Ambisinistrous.

Definition: Equally clumsy with either hand.

Usage: This word is the opposite of "ambidextrous," and it reflects the right-handed majority's bias that all things right-handed are good and dextrous, while the left hand is seen as bad and clumsy (see Etymology). It is analoguous to the construction "having two left feet," and it has a rarely attested synonym in "ambilævous" [æm-bi-'lee-vês]. By analogy with "ambidextrous" we may form an adverb "ambisinistrously" and a noun "ambisinistrousness."

Suggested Usage: The word implies a distinguished, all-round level of clumsiness: "To have dented both sides of the car during a single outing is a notably ambisinistrous achievement, Lancelot." A metaphorical deployment is also possible: "Dexter's ambisinistrous interpersonal skills have brought the Sales Department two lawsuits so far this year."

Etymology: From the Latin sinister, meaning "left," with the prefix ambi-, implying "around" or "on both sides." The left side was associated with bad luck and evil omens by the Romans, and their word "sinister" has arrived in English with those associations intact. The prefix ambi- has the sense of "on both sides" in "ambiguous" and "ambivalent," while implying "around" in "ambit," "ambulate" and "amble." It comes from the Proto-Indo-European prefix *ambhi- "both (sides)," of which the Greek equivalent is amphi-, which we see in "amphibian" and "amphitheater." In the Germanic languages, *ambhi- dropped its second syllable and became (among other things) the Old Norse um-, a prefix which contributed to a previous Word of the Day, the Swedish "ombudsman." And, taking another route through the same language family, it also lost its first syllable and acquired the sense "beside," eventually giving rise to the English word "by."