Bidet Mate!

If we're talking "Star Trek" style teleportation--let's head down to the transporter room, where someone else handles it and watches us dematerialize--then it would definitely be somewhere in México, probably in the Yucatan, or anywhere in the Costa del Sol. No checked baggage, no tickets, no aduana.

But if we could have a little handheld self-controlled teleportation device? Then the answer would definitely be "the bathroom." Worried you've got something in your teeth? Think your hair needs a combing? Need to pass a little gas? No problem--just teleport to the bathroom, take care of your business, and then teleport back to the party.

On the other hand, I would only use this if I could somehow verify that the bathroom was empty first. Maybe this isn't such a good idea after all.