Sometimes I slip up and call someone "sweetie" or "wab" (another nickname thorbol and I use for each other) when I'm having certain kinds of (extremely nonromantic) conversations.

He's the person with whom I can be most straightforward and opinionated. So this happens sometimes when I'm really getting intensely into a discussion. It happened once when I was discussing work with a coworker who was also a good friend. It only happens when I'm really comfortable with someone.