I grew up in Bar Harbor, Maine, a town where an inordinate number of cars and trucks have bumper stickers like this one:
Tourists can be a pain. Just one tourist can often be enough to get on your nerves, especially if they do annoying touristy things like drive slow, ask stupid questions ("Does the lobster stew have lobster in it?"), or fail to understand the concept of a 15% tip. When 2.2 million of them flood the island during the summer months, it's hard for locals to maintain their sanity. Sure, almost all of our businesses depend on the tourists who come to town and spend money, and because of this locals are usually more than willing to welcome visitors with genuine pleasure. But if you act like an idiot or an asshole, then I guarantee you will be mocked and ridiculed--if not directly to your face, then definitely after you've spent your money.
When I travel, I'll be experiencing the other side of this dynamic for the first time. I'll be that guy trying to absorb unfamiliar places and things. Hopefully I won't do anything that warrants open mockery, but at some point I definitely will be that guy who asks stupid questions and gawks at every street corner.
I'll be a tourist. But at least I'll tip well.