Mi casa es tu casa

Despite what you may have been told, the expression mi casa es tu casa is not that common. Upon entering someone's home for the first time, you're more likely to hear estás en tu casa, a formality which should be understood as meaning make yourself at home. A longer and more exaggerated version is estás en tu humilde/pobre casa. Welcome to my humble abode.

When mentioning their house in conversation, some speakers will refer to it as tu casa out of politeness. Or they might say something like por mi casa, que es tu casa, simply meaning: near my house. A beverage commercial turns on the potential confusion that this can cause for foreigners.

No olvides que aquí tienes tu casa is an offer, sincere or otherwise, for you to stay at someone's house the next time you are in the area. It's easy enough to understand this when you hear it, but it is harder remember to say it yourself with visitors.

Respetar la casa

Hoteles de paso, love motels, are a big industry in Mexico because unmarried adults often live in their parents' house and they can't have sex there with their boyfriend/girlfriend due to the cultural importance of respecting the house.

En tu casa

Since unmarried adults often live their parents, the notions of family and house are somewhat interchangeable.Oye, y en tu casa, saben de ti? Does your family know you're gay?

Casa de interés

Casas de interés are public/subsidized housing, the projects.

Echar la casa por la ventana

One way to say have a blow-out party is echar la casa por la ventana. Imagine the contents of the house going out the window. I've also heard this with tirarse.