I've had to hop off the bus after one stop (after realizing I'd forgotten something). Wasn't an issue for the driver.
Bus etiquette can be complicated. Stuff happens. There are places, and times, where I think it shouldn't be a problem:
Along a different route though, maybe the drivers deal with kids playing hop on/hop off/ring the bell at every single stop, games like this, and it does slow down the bus and disrupt service.
It helps to consider the context. Depending upon the type of route, are you making life difficult for the driver, or is he making it difficult for you? It's a little like how taxi drivers don't appreciate people getting in and asking to go only a couple of blocks. (If the passenger then pays by credit card, it means the small amount of payment goes to pay the cc company first, and the driver winds up getting nothing, or close to it.) So do taxi drivers want to waste time and lose pay by giving people one or two block trips? No. (Unless you tip.)
So you can't tip a bus driver, but avoid doing a lot of one-stop trips - unless it's pretty much certain the bus will be making frequent stops anyway.