The phrase "dumbest person" is used to describe someone who lacks intelligence or makes foolish decisions. It means that the person is not very smart or capable of understanding things easily. Full definition
There are a lot of dumb people all over the globe that buy just because of what they think is good. (autoline.tv)
There are dumb people who call themselves atheist, yet actually believe in a god anyway. (religion.blogs.cnn.com)
And yes I know, dumb people don't care about what people thinks beyond their own town (where they care a bit too much), imagine the rest of the world. (religion.blogs.cnn.com)