JC got Whiskas cat milk after he was weaned in the home he was fostered in. He turned four at the end of April, and is still getting it every day, because if I "forget" to give it to him, he wails until he gets it. And I mean wails - you can hear him a couple of doors down, and he can go on for hours. I don't think milk - even the lactose-reduced stuff - is good when given every day, because it probably means too much fat in his diet, but he seems to be addicted to it. It has to be the Whiskas brand, too. On the other hand, the only canned food he'll eat is brands with less than 1% fat, so maybe the food offsets the milk.
At my parents' house, nobody can leave a coffee cup unattended, because the cat will drink any coffee she can find - black, with cream and/or sugar, hot or cold. I guess that's worse than filching milk.