I'm surprised Facebook's showing irrelevant ads to you. The few times I have to use Facebook the ads are so relevant that it is downright creepy. They are known for buying people purchase history from credit card company, but they are still stuff I have not figured out how they made the connection, for example, I get ads for very specific product that family members with a different last name and who don't have facebook, bought recently.
It gets really spooky when you start getting ads for something that was mentioned a couple times in Messenger. Wouldn't be surprised if they are scraping DMs now, too.