You can call someone a meatball which would be like calling them a clown, fool, or someone wanting attention. It is the construction of "it up" that has most of us confused. Occasionally we say "it up" when indicating a way to be. Some examples: Live it up means you should enjoy your life more. Ham it up means you should act like a ham\clown. He was meatballing it up could mean he was acting like a meatball.

It's got nothing to do with eating. It probably means 'to make something meatball-y', so I'd guess that it's something to do with putting meatballs in a dish. It's tough to say without context, though.