I had the same thing happen to me at a Wal-Mart last year. I was on my lunch break and an old friend came up to see the cashier. She stopped ringing me out, and after all the hugging and high-pitched squeals they started gabbing. I asked her (very nicely and without attitude, I might add!) if she could finish my order because I had to get back to work.... Well out comes the attitude!!! She really started moving slowly then....
Sadly, it's not just Wall-Mart. Not much customer service these days. The clerks don't care if you buy anything or not.