Your name is Megan; you're a 25-year-old dark-brown haired Caucasian. You have very youthful features, which combined with your height (you're just barely 5" tall) and your flat chest, results in your often being mistaken for a 13-year-old. Every once and a while, in fact, someone thinks you're 10 or 11.
You don't want to wait to test the power of this sapphire, so you head for the mall. The sun has almost set by the time you get there, so you're going to need a ride home at some point. Hopefully, if this sapphire's magic works like it claims to, getting a ride won't be an issue.
You walk into the main foyer, and sit down on a bench by the waterfall. You take in your surroundings; and observe the people walking around here. It's time to formulate your plan. That guy you hypnotized earlier did exactly what you asked him to, without any hesitation, and without even realizing he was doing it against his will. He didn't understand why he did the things that he did, but he didn't question the fact that he did it.
This means that you could command someone to take their pants off in public, and they would do it as if they wanted to. However, they would still be embarrassed to be exposing themselves like that, and would probably immediately put their pants back on. Perhaps if you commanded someone to remove their pants and leave them off for the rest of the day, they would leave the area and go somewhere private.
You're not sure how this works, of course. You'd have to test it out, and hopefully you could command someone to forget about you, and then you'd run away, in the event that you screw something up.
Now, you're not sure if you could hypnotize everyone in this mall simultaneously, and you don't intend to attempt that. Most likely, the subject has to hear your command clearly in order for it to take effect. If you shouted a command in a noisy building like this, only some of the people would fall under your control, while people further away would be unaffected, and potentially run away and call the authorities if they see suspicious behavior.
Assuming your mind control can only affect the people whom you talk to directly, this means you will have to bring someone under your control subtly, without drawing the suspicion of onlookers. You certainly couldn't have someone bowing in front of you kissing your feet right in the middle of this crowded mall. Depending on what you wish to do with your subject, you may have to lure them into a private location with you.
Enough theorizing and planning. It's time to pick a subject. You take a look at the people in your immediate range of vision. Who do you select?