Skipping Out

Question: If I was tired from doing alot of activities and "skipped" out on something I promised my friend to go to, is that wrong?

Well, this actually deals with two things, promises and overcommitment, but both deal with one big thing...LOVE!
Our Lord tells us, "Let your 'Yes' mean 'Yes" and your 'No' mean 'No'"-Matt. 5:37. That means if you give your word to someone you should keep it unless it is entirely something out of your control like illness, death in family, etc. This makes sense in light of the Great Commandment, love of self, neighbor, and God (see Matt. 22:37-39).
When you say "Yes" to everyone and everything, it hurts you. It makes you overcommit, wear yourself out trying to keep your word, and ruins your reputation making you seem like a liar when you don't show. It hurts your neighbor because they expect you to be there and so when you don't show up, can cause harsh feelings. We all know how bad it hurts when someone stiffs you. It's not a fun feeling and I've known many friendships that have broken up because of being "stood up." Finally it hurts God because we are his children and image here on earth. Scripture reminds us, "They shall know you are my disciples by your love"-Jn. 13:35. If you constantly don't keep your word, people will see your actions as a reflection of God, thus as someone who is a liar. This is why Jesus states the second part of Matt. 5:37, "Anything more is from the evil one." It is the evil one that wants to stop love and cause hurt and harm.
Therefore, if you feel you may be tired or can't make it, just tell the person that. Don't make up an excuse and add fuel to the fire. Honesty is always the best policy. It will save a lot of hurt feelings and friendships. Also, don't forget to love yourself. You are not just some "work-zombie". Get proper rest and don't over extend yourself. I reflect on Ps. 46:10 quite often, "Be still and know that I am God." Sometimes being still is the hardest thing to do, but when we do it we can see God and our own humanity (we're no just human doings, but human beings), and that's something not to skip out on!