In Super Mario Bros.

Which size is actually meant to be Mario's default size? The small or the big one? Well, normally it's quite logic that the small Mario is the normal one and that he grows with the super mushroom. But if small Mario is really the normal standard Mario, being as big as all of us while Super Mario is a giant, then I ask myself why all the other characters in mushroom land are bigger than him. He's even smaller than these mushroom people and the koopa troopas. So, why is it like that? Or is Super Mario the default size and normal Mario is a dwarf?

YOU try doing the shrooms and see if anything makes sense.

Although to this, I would have to say that I've always noticed the same thing, and my conclusion was simple. In the original game, Mario has had his spine compressed from a barrel to the head in his previous adventure in Donkey Kong. (He seems to have proportion in that.) There is only one cure that doctors have been able to find to his cut down height, and that is the wild mushrooms in the mushroom kingdom. He leaves Brooklyn for them. The mushrooms cause an awkward change in size, and are weak to small doses of pain, but he becomes addicted to them and stays in the mushroom kingdom.

How's that for an Explanation?

How can he become addicted? He doesn't eat them, he just touches them. (If he had to eat them, then he would also eat the fire flower, the leaf, the frog suit, the feather, the star and: the mushroom that makes him small in "The Lost Levels", which makes absolutely no sense.) And since every contact with an opponent kills him, the explanation with Donkey Kong can't be correct.

"I have to get ready for this wedding, anyone have a fork and a knife? this suit is hard to chew."

Yep, I always eat my clothes when I change...

A mushroom is a food, a suit is a not a food.

Nevertheless, he doesn't eat it. That's a general misconception. If he did, then the poisoned mushrooms would make no sense: I accidentally run into a poisoned mushroom and become small. How shall I imagine this? That Mario accidentally ate that thing, although the two mushrooms look different? And there's still the question: What does he do with the fire flower? Eat it, too?
By the way, if you want a definite proof that the super mushroom only has to touch Mario to make him big, just look at the ending sequence of 1994's "Donkey Kong" for the old Game Boy. There you will see a nice non-in-game sequence that shows it.

Denny, lighten up man. Sheesh.