My morning coat, my collar mounting firmly to the chin, My necktie rich and modest, but asserted by a simple pin —
I noticed that several times in the poem he comments on his clothing—later he says that when he is old he will roll his pant legs—and this seems to be a way for him to describe how he perceives himself in the world. Though he is insecure about his balding and his thinness, he can use clothes, in this circumstance to help him feel more confident, but not too confident, as he only has a "simple pin."