Groupon's advertising failure should be a teachable moment for businesses because they highlight some important issues within advertising and culture.
There is a disconnect between startup and corporate culture
Startups and major corporations have two very different approaches to business and Groupon's advertising highlighted the disconnect between the two cultures. Startups want to be creative and don't want to be boxed in by the rules and regulations of the dominant paradigm. Major corporations play within a specific framework and have processes, procedures and guidelines that require strict adherence. The problem is that within that framework, you can create great advertising and Groupon at some point signed off on the ads believing that since they weren't "playing by the rules," their ads would create a memorable and lasting impression. The problem is that the memorable and lasting impression was decidedly negative.
Shock Value Never Works
I'm not sure of the dynamic between Groupon and CP+B (who created the ads) but at some point someone should have said "Wait a second, let's take a step back and see whether this actually helps promote our brand or whether these ads provide nothing more than shock value." Shock value is never an effective sales point and in this age of social media, the idea that any publicity is good publicity is not the way you should look at your brand. One could argue that shock value gets people talking but they aren't talking about your product, service or message. They are discussing, searching and gauging reactions.
Don't assume everyone will "get" your advertising
These kinds of ads are highly guarded secrets and I completely understand that. However if Groupon had a focus group of just 10 people, that small sample size would have been able to give them enough information to determine they had a serious problem. Businesses in general should never assume that customers will understand their message especially when you use sophisticated humor or puns or imagery. Focus on the message first then play with it. Don't create something then have to go back and try to add the message after the fact.