Or move the ad to the bottom of the screen, or have it ignore clicks within half a second or so after it loads. When I'm about to tap my most recent conversation, I'm not thinking about "better make sure an ad doesn't appear here." But if it does just before my finger hits the screen, I end up selecting the ad instead, when I clearly didn't mean to. It's bad UI design to have the meaning of a user action change unexpectedly, and having it happen for the sake of something like an ad just adds insult to injury.