We have all seen adverts for brands that you take with a pinch of salt, overselling their product to the point of ridiculousness so that it crosses a boundary and is closer to being amusing. Consumers know that they aren't buying an energy drink that will literally help them to fly but they get the picture.
Sometimes this tactic hits home and people take it for what it is but you always run the risk of going the other way.
By over selling a brand and making bold claims about the quality and how people will feel you are opening yourself up to criticism. If you brought out a pretty standard mint and said it is 'coolly refreshing' people could accept that, if you claim it is the most refreshing experience of your like and like being dragged naked through an Arctic Ice Storm people will expect something big, if they don't get it they will feel let down.
The risk of over selling or 'puffery' can actually lead to mistrust in your brand and put people off. Although someone might not expect the exact description you give, if you paint an extreme picture people will expect a strong reaction.
Those are the issues it might cause to your brand and nobody wants a negative opinion of their work but it is not the worst thing that could happen.
Your over hyping or over selling of a brand or product also runs the risk of crossing over into false advertising which can lead to legal ramifications and complicated law suits. If you make a claim that you can't substantiate then you could be in trouble.
This will also take into account the credibility of the campaign and whether it could make people believe it or not.
Brands like Carling played close to this line but cleverly left it up to the interpretation of the consumer rather than saying something specific about their brand and product. The Carling campaign of saying "Probably the best..." in different scenarios let consumers fill in the blanks. If they had said id was definitely the best lager in the world other companies would have immediately challenged them.
There is nothing wrong with having confidence in your brand but being honest is important in creating a strong brand that people buy into.
Nobody likes a boaster and quite often we like to see people that are too big for their boots taken down a peg or too, don't be the brand that people want to be knocked off its perch.