They don’t. Piercing jewelry is usually made from robust materials that are inert in normal conditions, like stainless steel, gold, plastics, and sometimes glass or gemstones. So, no, you don’t taste anything, just as you don’t taste a plastic cup, ceramic mug, or stainless steel pot.
Not all rich people are smart, and not all smart people are rich. Seems kind of obvious to me now, but it took me a long time to comprehend this.