[undies]

And then there is Infantilsm......

Paraphilic infantilism, also known as autonepiophilia and adult baby syndrome is a sexual fetish that involves role-playing a regression to an infant-like state. Behaviors may include drinking from a bottle or wearing diapers. Individuals may engage in gentle and nurturing experiences (an adult who only engages in infantilistic play is known as an adult baby or be attracted to masochistic, coercive, punishing or humiliating experiences. Diaper fetishism involves "diaper lovers" wearing diapers for sexual or erotic reasons but may not involve infant-like behavior. Individuals who experience both of these things are referred to as adult baby/diaper lovers (AB/DL). When wearing diapers, infantilists may urinate or defecate in them.