I was watching the latest ep of Tim Allen's new show "Last Man Standing". In the ep, there was an exploration of the idea of responsibility. Mostly from the perspective of the activities/things a person gives up when they become parents. The gist of the episode was that to be responsible your life had to be boring. Personally, I don't think that is true.
Now being responsible does mean sacrifice. It does mean thinking about the consequences of your actions for yourself and the people around you BEFORE you take said that action. Then you weigh the consequences of taking that action against the effect it will have on the people around/depending on you. If that effect is negative, you don't take that action. (Of course, this is operating under the theory that you actually care about the people depending on you.)
Here is the trick: not every action you take will have a negative effect on you or the people depending on you. And, you are not barred from having fun when you wish. You just have to be careful about what you do, and make sure the people depending on you are taken care of. Being responsible means that your fun doesn't negatively impact those who depend on you.
If you're a parent and want to go out, you hire a babysitter. Your child is taken care of, and you help someone make a little money. Now, there will be times you can't work around the consequences, and you'll have to say no to the things you want. But that isn't going to happen every time. If you plan ahead, it might not even happen most of the time. When it does happen, just remember the reasons why you need to say no: you care for a special someone, you need to keep your job, etc. These reasons will help you if your friends pressure you. And if they're really your friends and value you, they will respect your choice. Even if they don't like it. Depending on the class of friends you have, you may have to put up with some hazing, but they'll still respect your decision.
In the end, being responsible doesn't mean boring. It never did. It just means choosing your moments for fun carefully and planning the excitement into your life. You may lose some spontaneity, but you gain so much more. So please, be responsible but don't let that stop you from having fun!