Insofar as it is used to refer to a person’s sexual attractiveness (as distinguished, say, from his body temperature), I wouldn’t say it is a sin to refer to someone as “hot.” But it does objectify that person—things, such as coffee, are “hot,” not people—and should not be used at all if someone has expressed displeasure in being referred to that way. If someone persists in referring to another person as “hot” despite being asked to stop, then that is a form of harassment and the harassment can be sinful.
