Is My Phone Recording Everything I Say? Researchers Investigate
gizmodo.com
gizmodo.com
Another explanation might be: I just discussed a holiday and promptly got an ad for the exact island. The person visiting me probably uses Facebook, so FB knows we were together and knows where he went via location. Logical conclusion: people discuss intercontinental trips and hence: show ads.
Of course, when there are millions of opportunities for coincidences to occur, and when coincidences are much more memorable than non-coincidences, the chances that everyone has a couple of these stories is pretty high.
It'd be interesting for someone to make a browser extension which logs all the ads you see, allowing trends over time to be spotted. It would also allow hard evidence in a situation like this.
Seeing a "Flaming Hot Cheetos" ad just could also just be the Cheetos is pushing this variety on their existing customers.