At some point in their lives, everyone has received an invite to go somewhere that they did not really want to go, or do something that they did not particularly care to do. It may be dinner with an acquaintance with a spouse you can't stand, or an invite to a family reunion when you don't feel like dealing with your family. At some point, you are going to need to come up with a reason you cannot go to these activities. There are several common, believable excuses you can use and tailor to fit your lifestyle.
If you have been invited to go somewhere and do something, the first thing you should do is check your availability on the date and time. In some cases, you may not need to make up an excuse, because you already have one. For example, you have to work, or your spouse has an important appointment with a client that day and you need to stay home with the kids. In most cases, you can tell someone you have a previous commitment on the event's date or time without going into specific details about the commitment. Personal obligations, such as studying for a test or promising your boss you would work on a proposal all night, can also provide good excuses.
Not Feeling Well
Headaches, stomach problems and general ill health tend to make good excuses for not going out. You can tell the person inviting you out that you do not feel well in order to avoid going out with him. The only catch with this excuse is that you should refrain from doing something where the person might see you, or posting pictures of yourself at an amusement park on Facebook immediately after telling someone you could not go out because you had a migraine.
Blame the price of gas, your student loan, your car payment, your health insurance premium or your low-paying, entry-level job. Your bills are no one's business but your own, and most people won't press the issue if you say you cannot afford a night on the town. Of course, you always run the risk of someone offering to pay your way; then you will have to come up with another excuse.
Just because it's the truth does not mean it's not a valid excuse for skipping out on plans. It's OK to tell someone that you are exhausted, have to get up and go to work bright and early the next morning, are allergic to everything on the menu, need to clean the house, study or simply want to spend some one-on-one time with your significant other. Not wanting to go out is not a crime; as long as you avoid intentionally offending anyone, there may not be an excuse better than the truth.