When you lose contact with a close friend for an extended amount of time from a week +.
Sometimes a friend vacation is needed when a good friend starts to get on your nerves. Take a break and come back to a refreshed relationship. Other times your friend may take a vacation from you because they have entered into a romantic relationship and spend less time with you and more with their significant other. The most convenient use of the term "friend vacation" can be used to stop contact with someone who your just not that into but they seem very interested in you. Just let them know that you'll still be in contact but your taking a friend vacation from them to focus on something important like work, or school. Hopefully by the time you get back from vacation they have found someone else to pursue and you can remain in the friend zone right where you want to be.