When you think middle child syndrome, you should think Jan Brady (played by Eve Plumb) of The Brady Bunch. She is the archetype.
Jan was forever tormented by her older, prettier, more popular sister, Marcia Brady (played by Maureen McCormick). Marcia got all the awards. Marcia got all the boys. Marcia got the top dresser drawer. MARCIA, MARCIA, MARCIA!
Jan also had to constantly look over her shoulder at her younger sister, Cindy Brady (played by Susan Olson), too. All of the Brady girls had hair of gold, like their mother, true, but Cindy was "the youngest one in curls". Cindy's curls helped people forget that she wore braces in later years, but Jan's mousy hair only served to enhance the fact that she had to wear eyeglasses. Poor Jan!
Put upon, taken for granted, teased, and given far more emotional trauma than any other Brady Bunch member had to deal with, Jan Brady will always be my model of self-control. Were I in her shoes, I woulda snapped and murdered the entire happy clan long ago!