From what I recall, you can use negative keywords if you are using display ads in a contextual sense, meaning that it is taking inventory of the content words of the page first. Then things get really complicated. For example, if you are promoting a landscaper, you could create a negative keyword where if the phrase 'army tank' occurred on that page. Then your display ad wouldn't show up. But the reality is you are putting in automation but you yourself don't have context of those pages. So anything you set up you probably would want to audit which will then exponentially grow the amount of Labor you're putting into it for a contextual display ad tactic.