Still want to enjoy things that you used to like vacations? Dinners with friends or vacations keeping you from some social activities? If you are un- or under-employed you might not have the same amount of money you formerly earned. Or if you were forced to take furlough days or a pay decrease then there is just less money to go around.
As you parents used to say when you were younger, if they are really your friends then they won’t have a problem. True friends don’t want their friends to have financial problems. If you can’t afford to go on a vacation with friends then tell them. If you were living a larger lifestyle funded by credit cards and are trying to pay down debt, be forthright. People who only like you for your money or won’t accommodate plans occasionally so that you can do something with them aren’t your true friends.