How to Bring It Back
Surprise! When you're a grown-up, every night is summer vacation. Those same options that you had during long breaks are all still on the table until the day you die. Actually, I take that back. Once you're sporting a beard and driving around with a Domino's sign on your car, you should also plan on never playing hide and seek with the neighborhood kids again, so let's knock that off the list of ways to spend your nights.
Otherwise, remember that the fun of summer vacation wasn't the endless days watching TV or playing video games or "chatting" on "forums," although those are all great things to do. The fun of summer was that you were free from the routine that someone else invented for you. Are you bored with your life right now? Think like a kid. Find something new to do. Finding a new hobby or skill is like giving your brain a vacation from the routines that are boring you to death.
In fact, at the beginning of the year, David Wong actually challenged readers to learn a new skill set. It's that important to your not-turning-into-a-cranky-bastard development. The Cracked forum now boasts 55 pages of readers who took the challenge, not because they had three free months of summer to goof off, but because what else are you going to do? Watch Breaking Bad? Yes, obviously you're going to do that, but when it's over? You're going to need a new activity to fill the Breaking Bad hole in your heart pretty soon. That's what a new hobby/summer surrogate can do for you. I know I'm having fun with M*A*S*H this year.