The belief that
one needs to have gender identity disorder/gender dysphoria to be transgender.
Also the belief that one has to meet society's expectations of appearance and behaviour of their preferred
gender in order to be considered transgender.
Truscum
people usually don't think that transgenderism/transsexualism (two terms that they consider to be strongly attached to one another) is normal
human behaviour,but rather applies to a small minority of
people who have an innate or acquired psychiatric disorder. They also typically think of anyone who claims they're trans without meeting those criteria as a "transtrender", ie. someone who claims to be trans for the sake of being seen as "different", "special" or "a rebel".