Klutz, a noun, came to English from Yiddish in the late 20th century, and it has origins in the German klotz, which means a wooden block. In English, it refers to (1) a foolishly clumsy person, or (2) a stupid person, especially one who is socially inept. The word is more often used in the first sense.
The plural of klutz is klutzes. Dictionaries record two derivatives: the adjective klutzy, meaning foolish or clumsy; and the noun klutziness, meaning foolishness or clumsiness. And we find a few instances of the adverbial klutzily on the web.
Sometimes you’re a bumbling klutz. Other times you’re an unconquerable hero. [Durango Herald]
The device has plenty of metal inside and it sports a water-repellent nano-coating, so it should be able to get me through any klutzy days that I encounter. [Southern Pines Pilot]
I seem to be the biggest world’s biggest klutz. I reach to get the salt shaker and turn over my beverage. [Clarksville Leaf Chronicle]
I think her meekness and klutziness mask the fact that she’s capable of creating perfectly balanced dishes. [Entertainment Weekly]
Preparing for their second meeting, he painfully and klutzily inserts contact lenses. [Independent]