We are taught to observe the rules of the road. So, what do you do when the rules of the road are broken or redefined by rogue operators of rogue vehicles? You take the law into your own hand. I don't write tickets or give warnings. I just do my best to give such people a hard time in the 3 seconds we encounter each other on the road. Call me a vehicular vigilante.

Scenario 1: On smaller single-laned streets (one in each direction), drivers like to give themselves room from parked cars by driving in the middle of the street, half-and-halfing it over the solid yellow dividing line. If there are on-coming scooters, they expect the scooters will steer clear of them.
Scenario 2: Scooterers often use the opposite-direction lane overtake cars, such as those stopped at a red light, to get to the front of the line.
Scenario 3: When a red light turns green, cars and scooters waiting to make a left turn will often try to beat the incoming traffic. Scooters have a better chance of doing so because they accelerate faster.

My solution to Scenario 1 and 2 are the same. When I see someone ahead of me cross into my lane from the opposite direction, I ride closer to the middle line. Playing chicken usually establishes my territory and forces them back into their own lane.

For Scenario 3, if I'm at a red light and I see people at the other side of the intersection getting ready to make a left turn, I usually peel out of the stop position as soon as the light goes green. This gets me to the middle of the intersection before they get a chance to squeeze in a turn. If someone insists on turning, I let'em have it with my left thumb on the horn.

I have no problem making good use of my scooter horn either. It's there for a reason. Besides, mechanical and electric devices have shorter lifespans if they're underused.