In a bar fight, it's more effective to use an intact beer bottle as a weapon instead of trying to break it to use it as a knife like they do in the movies.

In fact, the bottles are a lot harder to break than you would think. It takes an impact of 40 Joules to break an empty beer bottle.

It takes considerably less energy to fracture a human skull than it does to break a bottle.

Therefore, a beer bottle could be used to cause a skull fracture without even breaking!

Strangely enough, a full beer bottle will shatter with only 30 Joules of impact energy applied to it.

This means that the best way to use a beer bottle in a fight is to finish the beer first, and then use the bottle as a blunt weapon.

The researchers behind the study that came up with this conclusion were the recipients of the 2009 Ig Nobel Prize. The Ig Nobel Prize is awarded annually to unusual or trivial scientific achievements.
If you want more proof, here's a video I found on YouTube of some drunk people trying to break a beer bottle and failing.
Notice that the guy in the video is wearing helmet, and he still gets hurt. (Warning: the following video is incredibly stupid)