Beer is a mass noun and can not be pluralised, just like sheep, deer, water etc. When talking about beer in bottles or other containers it is generally accepted to say beers in reference to the container. More correct would be to pluralise the container it self such as, "we will have 3 bottles of beer" and not we will have 3 beers. Beers is also correct when referring to a variety of types. An example is "I like Canadian beers". As for the jack ass from Toronto, I hope he takes that attitude to Nova Scotia and a Nova Scotian cracks a few bottles of beer over his head.