How long have you had the bearded dragon?
If it hasn't been but a week or two he or she can still be getting used to the new environment, causing the grumpy attitude. I have often heard, and not sure if its true still or not, that taping brown paper bags on all viewing sides of a dragon enclosure for a few weeks to a month help them to calm down, especially with just one person feeding and cleaning the enclosure as needed.
Just like people, bearded dragons have unique personalities.