When I was a teenager I had three jobs:
1) Conveinience store clerk: AWFUL... don't do that, there are cameras pointed at the staff in most stores and people are *******s to cashiers at 7-11 type places.
2) Movie Usher: This job was pretty sweet, you could be alone at lot if you wanted to be, or you could work a lot with other people. There is box office, which is pretty secluded, projection, which is awesome, concession and ticket taking. It's easy-peasy and SA approved. Plus you get free movies
I think any job you get depends on the boss and co-workers you have... but some are 'generally' easier for the shy inclined.
Oh and 3) was as a paintball arena attendant... which was the best job EVER! (except for my current one) You might wanna try for a small business type job if you don't want the "typical" teenager job. If you can get a gig at some random small business that would be really good, because in my experience small business owners are usually pretty lax and cool,so you'll feel realxed and calm, and will have a good experience.
Hope that's helpful! Stay away from convenience stores!!! BEWARE!!!
and GOOD LUCK!!