I have one word for you - inertia.
Please remember that, while you have a seat belt, we your passengers do not. Heavy acceleration and sudden hard stops not only toss us around like rag dolls, they also reduce fuel mileage and increase wear on these old busses. Most of them are barely running as it is.
Seriously. Knock it off. I have pointy sticks; if I have to chase my yarn all over this nasty wet floor one more time because you've slammed on the brakes again, I shall have to use them on you.