antisocial

Antisocial means harmful to other people, or simply avoiding their company. The word does both jobs and they are not the same.

The serious sense is about behaviour, and antisocial behaviour is a formal category in British law covering noise, vandalism and intimidation. The mild sense is about temperament, and calling yourself antisocial usually just means you would rather stay in. Psychiatry has antisocial personality disorder, which is a specific diagnosis and not a synonym for shy. American English often writes it without the hyphen, and British English uses both forms.