what does this mean "Or what is he of basest function, that he says his bravery is not on my cost- thinking that I mean him- but therein suits his folly to the mettle of my speech?

This again means that Jaques pits his humor in making generalizations about the people in the court, or by making it seem as if his jokes are general in nature. If someone protests his words, Jaques says it's because they're admitting he's talking about them........ that it isn't wrong of him, but rather the oerson who through his interpreatation of his words is admitting they've done wrong.