This quote means that humans can always find a flaw in someone else in order to make themselves bigger than others. People refuse to let go of flaws, they believe in an idea of perfection and so we say blue eyed blondes are beautiful versus saying we are all beautiful in our own way.
In simpler terms, we refuse to see our differences as perfect.
Perhaps Dunbar uses the image of a mask as wearing a face allows us to conceal our face - enabling us to hide any expression or emotion. In his poem, he mentions how black people felt the need to appear as content or happy when surrounded by people who were white - especially when they felt the opposite. The mask represents the false expressions the blacks had to wear.
Uhhh you gave him luncahbles and he didn’t like them
