Mi casa, su casa

My friend Mike is visiting for the weekend, and I just got off the following quip in response to his polite request to take a shower: "Mi casa, su casa -- which reminds me: Can I get your half of the rent?"

However, maybe I shouldn't say things like that right after people wake up, as he frowned and looked a little worried for a minute until I explained that I was just trying to be funny -- you know, exploring the implications of the saying, the responsibilities that come along with the privileges and all that. Still, I thought it wasn't bad for first thing on a Sunday morning.