The customers. Everything is an emergency when it comes to the customer's iPhones. They want their phones fixed, and they want them fixed now, which for some reason causes your average consumer to lose their humanity. People assume that it's Apple's fault that they dropped their device in the toilet (90% of the water damaged phones), or that the screen was faulty because they dropped it 10ft onto the concrete and it cracked. Everyone else in line be damned, they're time is more important and they demand to be seen first. People also don't understand the very basic principles of a warranty. "I know it's out of warranty, but my 5-year-old phone isn't as loud as it used to be. I didn't do anything. Apple should replace it for free."
The FRS is not only responsible for taking these iPhone appointments every 10 minutes (a very demanding time limit per appointment), but are also tasked with teaching One-to-One customers with 30 minute and 1 hour personal training sessions. The amount of knowledge you're required to absorb (mostly on your own time since Apple is only really interested in teaching customer service during training) is immense, and insures that you'll be discussing work-related issues during your breaks.
You have no downtime with this job. On one hand, the day goes quicker when you're shotgunning tech support to 40+ customers, but it gets taxing. The front of the store (normal "Specialists") who are tasked with working basic sales and the like, are given as much time per customer as they see fit. If you want to spend your days interacting with your coworkers rather than rushing through appointments, take this job instead. It pays a dollar or so less, on average, but is an entirely different experience when it comes to working at the Apple Store.
Also, the hours are erratic. As a part-time job, the FRS position takes up ALL of your time. This is because you're scheduled only a few hours per day, almost EVERY day. It's hard to predict what your hours will be, week to week, which makes it impossible to schedule something in your free time. You have to give a minimum of 3 weeks notice to get a day off, and it's not guaranteed that they'll give it to you. On top of this, all the other FRS's are working a minimum of 5 days a week, and because Apple has to pay time-and-a-half on the 6th day, nobody else is allowed to cover your shift.
