Worry not, nitrogen is perfectly safe. In fact it already makes up 78% of the air we breathe. Nitrogen flushing is a very common process in the food industry - if you've ever opened a bag of perfectly crisp chips, you've enjoyed the benefits of nitrogen flushing!
So go ahead and stock up on Hangover Coffee without any fear of it going stale. It's a good feeling to know you'll never be without fresh coffee!