Someone who's very abrupt — so blunt or curt that they're almost rude — has the quality of gruffness. Your uncle's gruffness might cause most of your cousins to be scared of him.
Someone who's known for her gruffness isn't necessarily mean, but she's so direct and matter-of-fact that she can come across that way. Gruffness isn't a great quality in a kindergarten teacher, but gruffness can come in handy when you work as a military officer or a dog trainer. Gruffness comes from the adjective gruff, which means "short or surly," but originally meant "coarse grained," from the Middle Low German word grof, "coarse, thick, or large."