A woman and a kangaroo wearing a diaper walk into a McDonald’s, and the woman says: He’s my service kangaroo. No, it’s not the setup for a joke. But it may be a sign of the times. In a culture that has increasingly embraced animals as an extension of family, the kangaroo incident earlier this year seems to be part of a growing problem. With pigs flying — literally — aboard passenger flights, monkeys cruising the grocery aisles and large snakes hanging out in restaurants, the issue of what’s legitimately a service animal for someone with a disability can get murky.