Well this is something my friend and I sort of came up with. Tamanegi means "onion" in Japanese. And so we joke and say Tamaki is an onion. =]
And since he's a coward some of the time, "Tamaki the cowardly onion" was devised, and now I've turned it into a whole oneshot.

There was once a cowardly onion called Tamaki. He was so cowardly that he was even afraid of himself! The strong stench that onions usually give off and how it causes humans to be teary eyed - Yes, Tamaki was in fear of that. He would cause his very self to cry.
He was so cowardly that all the other onions and vegetables would laugh at him.
The meanest of them all was the dreadful, evil eggplant called Nekozawa. He could think of the nastiest insults to say to poor cowardly Tamaki.
But then one day, the cowardly onion Tamaki met the sweet okra, Ayu. She never laughed at Tamaki at all, and was his only friend. It consoled him for a while.

One day, Nekozawa the eggplant came and pushed Tamaki over the kitchen counter! All the vegetables roared with laughter as the cowardly onion hit the hard floor. But Ayu the okra turned to Nekozawa and scolded him for doing something so cruel.
The evil eggplant only jeered at her and walked away still laughing.
Ayu wanted to help poor Tamaki! But she could not get him back on the counter all by herself. She sat in despair for a moment. Then, the tall and handsome green pepper Kyouya came over to Ayu. He offered to help her bring Tamaki back up. The two twin radishes called Hikaru and Kaoru came over. Along with the green leek Mori, the baby carrot Honey, and Haruhi the brussels sprout.
They were all none other than the famous Ouran Vegetable Club! And with the help of Ayu the okra, all seven of them helped pull Tamaki the cowardly onion back onto the kitchen counter.
Nekozawa the eggplant came over and jeered at Tamaki again. But Haruhi the brussels sprout smelled so bad that Nekozawa and all the other vegetables had to pull away from their teasing of Tamaki.

Tamaki humbly thanked his rescuers for saving him. And, something incredible happened! The Ouran Vegetable Club made Tamaki their leader, their king of the famous Ouran Vegetable Club! Ayu the okra joined as well as Queen of the Ouran Vegetable Club.
But regardless, Tamaki was still a cowardly onion. Even though, after this, he enjoyed bragging to the eggplant Nekozawa that he was a "king."
However, the evil eggplant had something else in mind. He and a few other unpleasant vegetables withdrew to the very back of the counter. And there they formed the Black Vegetable Club. Dark were their intentions, and evil their purpose. Kyouya the green pepper learned of this and informed Tamaki. The cowardly kingly onion declared that they would do war with the Black Vegetable Club.
The two clubs met on either end of the counter, ready for the fated duel. Some of the vegetables were still undecided of which side they were on, so they hid behind the various objects on the counter and watched in awe.
But then, a tragedy occurred. The human decided to make a vegetable stew today. So, neither side won the silly war. It was won by the human.
The human chopped and threw all the vegetables into a big pot of water. And well...in the end, they were all good for something: they had helped make a delicious stew!