Si estás hecho polvo - if you’re made (into) dust - then you’re ground down, exhausted, knackered, whacked. And si haces polvo a alguien, then you make someone (into) dust, meaning you wipe the floor with someone in a competition. Look up the phrase echar un polvo and you’ll see the definition realizar el acto sexual, whilst if you say someone has a polvo - alguien tiene un polvo - it means you find them sexually attractive. There we have it; many shades of grey to this dust.