Final answer:
Frotteurism is the act of gaining sexual gratification from touching or rubbing against an unwilling person, classified as a paraphilic disorder.
Step-by-step explanation:
Touching or rubbing up against an unwilling person is called frotteurism. This behavior is a form of sexual assault and involves gaining sexual gratification from touching or rubbing against a non-consenting person, often in a crowded public space. It is considered a paraphilic disorder, which means it is a type of sexual disorder characterized by recurrent, intense sexually arousing fantasies, urges, or behaviors that are outside the range of normal sexual activity and can cause distress or impairment in social, occupational, or other important areas of functioning.