Entirely disallowed? I've had to use my horn while stationery for safety reasons. Like when I'm in a parking lot, I can't go anywhere because there's a car in f

Entirely disallowed? I've had to use my horn while stationery for safety reasons. Like when I'm in a parking lot, I can't go anywhere because there's a car in front of me, and someone starts to back out of a parking space toward me without looking. They need to know that it's not clear, and that's what the horn is for. (It's also what their mirrors are for, but I can't control that.)