RSVP is an abbreviation found on most formal invitations in America. RSVP stands for the French phrase "Repondez, s'il vous plait." This tradition occurred during the end of the nineteenth century and the beginning of the twentieth century when American wealth fostered an interest in all things European, including painting, poetry and written etiquette. Responding promptly back in those days was imperative as six course meals were common. Nowadays, if you want your RSVP to be memorable, consider creating an amusing RSVP.
Write down phrases for "Yes, coming" and "No, can't come" that are amusingly sarcastic. For example, phrases to the effect of "Yes, I'll be there. I have nothing better to do that day." Or "No, I'd rather lick my kitchen floor."
Write a positive RSVP that sounds halfhearted such as "Yes, I guess so" or "Might as well." For negative RSVP, you could write something to the effect of "Getting my dog's teeth scaled" or "Waiting for the cable guy that day."
Write a positive RSVP statement that focuses on the food and beverages (rather than the people in attendance) such as "Yes, we'll be there; we love to drink until we fall down, especially when someone else is paying." Or "No, I remember the food you served at your last party. Yikes."
Choose the phrase you like best and that you think will be least offensive.
Make a list of simple phrases for "yes" that are charming in their simplicity and have a slight amount of humour. For example, on your invitation for "yes, coming" you could have: "Hell's yeah" or "Can't Hardly Wait (just like the movie)".
Make a list of "no, can't come" phrases such as "Oh, hell no" or "You betcha, NOT!" or "No, honey, but you can call me sweetheart."
Choose the phrase that you find funniest and most appropriate.