How does one say 'no' to a party invitation, when one has already said yes

[Magrat]

because you were caught off guard

and not just yes, but 'yes how lovely, we'd love to come'

but we have too much on over the christmas break and DS is really acting up and we have a lunch invitation on the same day as the late pm / early evening invitation and I think it's too much .. and I don't really want to go either

Feign illness? That's what i'd do. What else can you say really?

yes i think you have to lie tutut

D&V always a good un lol. They will ask you not to come!!

I don't know...if you feign illness, you won't be able to contact them until the last minute and by then you may have put them to some trouble. If you contact them now and say "I am so sorry, but I did not realise I already had an invitation for the same day" you will not only avoid lying, but also may safe them to going to unnecessary trouble.

Perhaps your dh has booked a table at a restaurant for just the two of you, as a Christmas surprise?