What does a pineapple stand for?

It means that they are "swingers" if you believe the urban legend. Most swingers do not use this metaphor as there are plenty of places to meet and greet, but are amused by the urban legend that is spreading around.

PineApples are historically symbols of welcome and hospitality.

This is what the pineAppler wants you to believe. It actually means that the inhabitants, now victims, have already been turned into new universes and succumbed to the pineAppler's ultimate weapon, the painApple. It is best to run away from these houses as fast as possible for if the pineAppler believes you have been tampering with his property, you will be next, and only the meatballer, who is currently M.I.A. will be able to save you