def stoopid(word, extra=None):
    """
        Return a 'StUpId' rendition of word. Optional, `extra`
        argument to randomly flip case of a small proportion of letters
        after the first pass, for an 'EXtRa sTupID' final form.
    """
    if not isinstance(word, str):
        raise TypeError(f'argument not recognized as string: {word}')
    new_word = ''
    for i, item in enumerate(word):
        if i % 2 == 0:
            new_word += item.upper()
        else:
            new_word += item.lower()
    if extra:
        pass
    return new_word
