Unplanned sexual encounter, usually hurried to the point where it is generally done while mainly clothed.
Intense sex between two uninvolved persons, where the amenities are ignored.
Foreplay is generally absent from such encounters.
Noteworthy: Mutual sexual intercourse, where anonymity is the standard.
Frantic sex, where foreplay is often ignored.
Minimum nudity is the standard, as just enough clothing is loosened, in order to accomplish the sexual act.