My (youtube) hack is pretty simple: when I see an ad that has really terrible targeting, I click it. Not only that I go into the settings and I click "show me more like this" (incidentally this is a great way to see that 90% of ads are completely miscategorized, kindof makes you doubt the whole system). In periods where I'm more diligent about this I've successfully reached a point where over half of my ads are Chinese-language.