decline it

“Where any doubt exists in reference to your ability to accept an invitation to dinner, it is usually better to decline it at once, unless peculiar circumstances exist; but for an evening-party, it is as well to accept it, and if circumstances arise to prevent your attendance, you should send a polite note of explanation and regrets, as soon as possible.”

A Manual of Etiquette with Hints on Politeness and Good Breeding

“Infelicity is involved in corporeal nature, and interwoven with our being; all attempts, therefore, to decline it wholly are useless and vain; the armies of pain send their arrows against us on every side, the choice is only between those which are more or less sharp, or tinged with poison of greater or less malignity; and the strongest armour which reason can supply will only blunt their points, but cannot repel them.”

Samuel Johnson