I don't think you did anything wrong. I hate when people don't acknowledge you at stores. It's our company policy at my job to always acknowledge the costumer. When they say thank you we must say "My Pleasure."

On a side note, one lady once told us that we were too nice and cheery to our customers and complained about that. Just the other day some kid filled out a comment sheet (to tell us how we were doing) and complained that it was rude to our customers to be closed on Sunday because of tradition.

Basically, the customer is always right and if you didn't get the service that you expect and deserve, all bets are off.....
The thing is not to make yourself look like the "p.o'd" consumer.
This is something that causes us trouble at work. No matter what WE think we always give the customer what they want. One a-hole complained about his food being "too cold" when in fact everything just came up completely fresh and HOT.
He was sent BOG's (Be our Guests, free coupons) and ripped us out of money.