Personally I was surprised "How can FB be such a dumbass?"
More than once I have bought something online, just to start getting ads for the same, specific product I had just bought.
This hasn't been an issue though, until it was showing ads for a product I bought for my wife. I'm showing off something to my wife and "boom" FB is promoting a product I would never personally use.
Luckily she didn't notice that.