[Cloud]

it depends. "in social situations" covers a lot of ground. In formal written correspondence, for formal events, a courtesy title, whether it's Mr., Ms., or Dr. is expected. In less than formal encounters, it still depends. Depends on setting, on age, on the amount of respect the addressor wishes to convey.

For an addressee, in the United States, it's almost always pretentious to insist on being addressed with a courtesy title.