Try clicking the little red X in the upper right-hand corner of the browser window.
Seriously, though, I've lost all patience with the web. When I run into any of that kind of crap that even moderately annoys me, I just close the tab and move on.
Auto-play audio/video? Close tab and move on.
Pop-over dialog entreating me to subscribe to your newsletter? Close tab an– wait, for this one it's actually: enter some variation of "pop-ups still suck and now so do you" formatted as a valid email address, then, close the tab and move on.
I will admit that I go out of my way to make sites I like less annoying enough that I can actually stand to read them, but for everything else, I just close the tab and move on.