Chicken beaks can be hard and painful if they manage to hammer you on bare feet. Or if they come up behind you and peck at a sore on the back of your leg that is just beginning to heal. Or try having your eye pecked. Ouch. No. Don't try that.
Chickens use their beaks for everything since they don't have hands. They use their beaks to communicate, investigate, fight, and to eat. Often when they peck at bare feet, someone has colored toe nails or a freckle or a scab that the chicken is attracted to. The last thing to suspect when a chicken pecks you and it happens to hurt is that they do it to be mean.
A couple of my friends have come by to see the chickens wearing sandals. My chickens are very curious about bare feet because they don't see them often as I always wear shoes. My friends never come visit wearing sandals a second time.