Edward Elric doesn't like being called short.
Most people find this out within the first few moments of their meeting, because it is the first observable thing about him—that he is small, small next to the armor-wearing individual next to him, and small next to just about anything else as well. (The second observable thing would probably be his heated temper, but Edward has always been an emotional individual.) It is what people say to him because they cannot think of any other way to relate to him, this boy who has the heavy title of 'Fullmetal Alchemist', a title that hardly seems to fit him when the huge man that follows him around is so much better suited for it.
He hides the reason for the name, of course, not so much because of fear as because it's less troublesome—not so many questions when his metal limbs are hidden, after all. So he wears long sleeves and gloves, and no one sees anything to ask about. But when he is fighting, he takes the first opportunity to shed those extra layers, to give himself room to move and to keep the material that forever sticks in his hollow joints from bothering him further.
Seeing Edward Elric in action might even be considered inspiring; his mastery of alchemy has exceeded the known bounds of the science, so that he no longer has to even use a transmutation circle. He has perfected the use of his namesake, the two automail limbs on either side of his body; he knows the limits of his humanity and surpasses them with the mechanical parts of himself. It is when Edward is fighting that one can see why he is the Fullmetal Alchemist; it is then that one realizes that small frame can support such a name.
But there is still a name that Edward dislikes, and that is 'chibi', or any other form of 'tiny'. And while it grates on him simply because he knows it is true—he is small, and short, and he has been small for much of his life—that is not the only reason Ed hates to be called small. He rarely thinks about it consciously; he never mentions it to Al, or anyone.
Until the day he can shed his metal limbs, and his heavy name—until the day that he restores Al's body and his own—Edward cannot grow. Physically, because his arm and leg, installed with such care, suppresses his growth; spiritually, because he refuses to move on in life without his brother; mentally, because he cannot think about anything but his goal—the Philosopher's Stone—without risking losing his control over his life.
He does not think about it, but sometimes, being called short is a heavy reminder of why he carries himself forward.
Someday, he will be wiser. Someday, he will be stronger.
And that day, he will walk arm in arm with his brother, who will smile at him, and stature will be forgotten for love.