Some big brands are getting a reminder of how thin the line is between edgy, buzzy ads and deeply offensive marketing. General Motors had to scrub a Chevy ad soundtrack of 1930s song lyrics loaded with Asian stereotypes. And an online Mountain Dew spot ignited a firestorm of criticism after it ran an ad suggesting black men are violent thugs. Parent company PepsiCo apologized and took it down.

The neon green drink walks a tightrope trying to make ads that will break through the clutter to get young caffeine hounds guzzling. It’s a long way down when an ad misses and offends the masses, even for a brand that aims to be provocative.

“Mountain Dew is not the Gap. They’re not Ford. They’re not a sort of traditional mainstream brand,” says Wharton School marketing professor Jonah Berger, who is skeptical of Mountain Dew’s apology and ad removal, since it’s still widely available elsewhere online. “They get credit for it among the segment that they want to appeal to, while also telling other segments, oh, well, we have nothing to do with this.”

Even when advertisers aren’t intentionally trying to offend, it’s easy to go too far in the effort to stand out online.

“Sometimes people sort of try to extend the risk factor in order to get as many impressions on their message as possible,” says Geoffrey Colon, vice president of digital strategy at ad agency Ogilvy & Mather.

Agencies have to turn out web ads much faster to keep up with online trends.

“Digital agencies create content under much tighter deadlines,” explains Advertising Age reporter John McDermott.

There’s another potential risk with online video. Compared to television ads, fewer people may screen it before it goes out into the world.

“The TV station tends to screen television ads,” points out Avi Goldfarb, marketing professor at the University of Toronto.

But online videos go straight to the public via the company’s website, YouTube page and social media.