While I agree, generally that we all may be accused of having a "bad" day from time to time, when this happens at my place of work we get called on it. This is particularly true if you're in a customer service role.

I think if you need to read a book or surf the web for downtime you should go somewhere (other than sit at a gate or behind a desk in the middle of the airport) to get your downtime rather than trying to do it in plain view of customers and then try to avoid responding to their needs. That would be my constructive advice if they worked for me. Don't they have a staff room or something?