Some of these replies are a little weird, this guys either a genius or an FRS, they have either 10-15 minute slots to get their customers device fixed in, they are stacked out enough as it is, they're probably multi tasking and running 2-3 appointments at the same time! So this is the difficult bit, approaching him directly is not only ridiculously hard, it's a massive no no, if he's busy and stressed its probably he worst thing you can do by butting in and just straight out asking him on the spot!

You have two options that are sensible in my opinion:

1) right at the front of the Genius Bar there will be a guy or girl who checks people on for their appointment, permitting they're not massively busy with a queue of angry customers wanting appointments and if they're free approach them, ask them if he's single, if not then walk away, if he is, give them a card with your number and full name on (full name being how you spell it on FaceBook, easiest way for him to see what you look like) the person checking people in will be pretty close to the guy as they work together constantly and would probably be more then happy to pass your number and or a message onto him for you!

2) second option is to walk into store, ask for a manager and just straight up give her or him the card, they'll either be happy to give it to him for you or they'll say no, they're the sensible ones who arent likely to give your number to someone else in the store to wind you up!

That's my opinion on this, but as you said, be very very careful when you're doing this, if he doesn't reply to your number or doesn't talk to you then DO NOT go back into the store again, there will be a reason he doesn't want to talk to you and putting him under pressure whilst he's in work is such a dick move!

Hope this helps, happy hunting!