Tthis almost feels like a silly question, but I will ask anyway.
I'm coming over for just two days. The purpose is a job interview and just to check out Bahrain. I intend to get my visa upon arrival siting tourism as the reason (I will present a US passport). If I mention a job interview will that cause any issues? Is it best not to mention anything related to work? Should I not say I'm considering moving there and wanted to check it out to see if I like it?
Just say you are coming for a short break. Don't mention interview. It won't make matters worse but may complicate. You NEED an address where you will be staying in Bahrian and details of your return flight for your disembarkation card. Fill this in before queuing at customs
I know it differs on a case by case basis, but for US passports, they don't usually ask WHY are you here. They may ask where are you going to stay or for how long - all these information is written on the card you will fill in anyway. And as Jo rightly pointed out, you should do it before you queue otherwise you will have to queue again if you don't have this Card in hand. Just let us know if you need anything when you arrive.