[Dondoh]

If someone is intentionally failing to tip there is nothing you will say that will really encourage her.

In the case of the person (or persons) who fails to tip out of ignorance of tipping customs, it is pretty easy to pose a question to the table like; "I wonder how the custom of tipping when you win the pot got started? It makes alot of sense doesn't it? The winners pay the dealers salary and the losers don't have to feel bad about not tipping."

That way you can indicate proper etiquette without insulting anyone.