They are extremely territorial
Anyone who’s owned a dog understands that, for the most part, they’re very protective of their owners. A cute bark, maybe a snarl, it’s all actually kind of cute. But with these guys it’s a whole different ball game.
Tibetan Mastiffs are known to be very “thick headed” and will not budge when they’ve decided they’re going to protect something. Whether that’s their owner, a toy, or their territory, you best be turning in the other direction unless you want a swift claw to the skull.