Those bare feet are disgusting and so unprofessional. Flip flops are not adequate in workplace, unless you work at a beach bar or something like that, clearly not the case. Surprised Apple allows it.
Actually, flip flops are far healthier than socked and shoed feet that is common in the Western world. In Asian countries, flip flops and bare feet are far more common than socks and shoes. The "disgust" you speak of us a societal thing more than about actual cleanliness.