You should also be aware that the ads are almost always related to something you have Googled at some point. (Though, sometimes, just barely.)
I googled my pickup truck model, exactly once, and I saw ads for pickups for months.
Usually the ads I see are programming-related, though. Right now I’m seeing an ad for “Apigee API Management” software. I have no idea what it is, but I suspect it has something to do with web programming — I’ve been writing some documentation for a binary Tcl/Tk extension I’m designing and have done a lot of Googling around CSS properties in the past weeks.
So if you are searching pretty girls or just looking through dating sites... that might be enough to get you an ad like that, LOL.
That's what really ticks be off about recommendation services (which ads are a subset of). Sometimes I see something on Steam that looks vaguely interesting, and just when I'm about to take a closer look I think "do I really want to see recommendations for similar stuff for the next three weeks?" And the answer is usually "nah, not worth it".
There are many ways to keep from getting suggested content. You have to go through several settings, including your browser settings, to keep from getting an "advertising ID". This way, ADs will usually not be based off anything you do. Whatever advertising that is targeted to you can be removed by clearing your cookies. Moreover, in Chrome, you can stop websites from giving you 3rd party cookies, which, for me, has stopped any advertising based of my actions.