Brian's solution worked.

Thanks to all of you who offered advice and/or confirmation of the best way to get into my bathroom. Turns out it is indeed a push-button lock which easily popped when I used the inside of a ballpoint pen (the ink thingy) to poke in the itty-bitty hole. Now you should all be a lot less worried about my kitchen sink (which, I assure you, was scrubbed and sanitized immediately after doing yeoman's pee duty) and, instead, concern yourselves with the fact that I could walk in on you in the bathroom the next time you come over to visit.

Dinner on Saturday night at my place, then?