FYE is extremely well known for having shitty compliance when it comes to promotions. Also, it seems like they're trained to be scratch nazi's when it comes to checking items. I had 3 things that were rejected yesterday. Two had hairline scratches (that you couldnt feel) and were about as long as half of a fingernail. The other item was rejected because it had DUST on it.
In surprising news, I was able to just bring in my ipod touch and show them the twitter page and they let me use the coupon. I was buying an item that was $39.99 regularly, on sale for $14.99. When they input the 20% off "regularly priced dvds" coupon before scanning the item, it rang up as $34.XX after tax (20% off the regular price). When they scanned the dvd, and then input the coupon code, it took the 20% off the sale price ($12.XX after tax).
So, if you plan on buying sale items with the 20% off coupon, just make sure to have them scan the item, and then mention the coupon.