Maybe there should be muzzles for chihuahuas. The breed is at number 2. Fiercer than a Jack Russell, so there ! Had two chihuahuas, no sign of aggression, but we had a papillon (mentioned as a "breed known to be aggressive") that was so protective that it would pick a fight with any and every breed; it lost an eye and got a broken rib in fights, but was undeterred by these reverses, never won a fight, and stayed just as bad as before.
It did try to pick fights with the wolfhounds, but they never noticed ! They were vaguely aware of a noise somewhere near their 'ankles', would look down at this bouncing, snarling, midget, to see what it was, and disdainfully look away again.