Those guys really made me furious when it came to the bill. The waiter added a generous 18% "gratuity" to the invoice for the three of us - without asking.
When I asked if this is a sort of special treatment for tourists, he seemed really uncomfortable and claimed this is "way of helping people out" - because this way they would not have to calculate the tip. He said that they did that with every customer - not only tourists.
When we left the restaurant I checked one bill on another table - guess what - it did not have the gratuity on it.
While I do understand that some tourists might not understand how tipping works in the US (because in many other countries tipping waiters is voluntary - because waiters get paid a decent wage and do not depend on tips) - I do not accept to be treated in any other way than locals. There are many restaurants who find better ways to deal with this, i.e. by adding a little description on the bill or menu.
Btw the food was okay but overpriced - comparing to other places we have been to in that area.