If you're awkward and clumsy, you can call yourself a klutz. If a klutz is carrying a tray of full glasses across a dining room, you can be sure they'll end up on the floor.
This informal word is perfect for talking about a goofy oaf who trips over his own feet and seems to drop anything he's holding. You might say, "Don't let my brother move your TV — he's such a klutz!" Klutz is the Americanized version of the Yiddish klots, which means "block or lump," and also "clumsy person or blockhead." A related word in German is klotz, "boor, clod, or wooden block."