And in some perfumes is there more delight Than in the breath that from my mistress reeks. (lines 7-8)
So maybe in the 17th century no one's breath smelled that amazing. This is a long time before mouthwash. Still, this criticism seems a little harsh to us. It's one thing to say that someone's lips aren't coral red, but quite another thing to say that she stinks. Shakespeare is pushing the satire just about as far as it will go, dissecting everything about this woman's appearance. After this, he starts to pull back, and the next line is much sweeter: "I love to hear her speak" (line 9).