Sarcasm is also used in a lot of dry humour. Emotionless, joking at the expense of others, but coming across as all serious.
I've been known to coldly scold (oxymoron.. LOL) someone, and they haven't even noticed, any yet someone else has intervened and said, "That was harsh".
I'm also well aware that most of the time it is most unwelcome, but sometimes I become so enraged or just fed up with the direction a conversation or action is heading I end up mocking the person, and convey this in a way (or I try) so as they don't even notice.
It amuses me sometimes to have a laugh at "their" expense, and see them not realise.