I'm going to have someone drive over an hour for nothing
Why, though? Are you trying to get back at this person for something?
I told them to come over on Sunday, but I'll be busy getting ready for a party.
If you plan to waste someone's time when they have driven a long ways, you are treating them rudely. You should call them and explain you won't be available so they don't make the trip for nothing, and apologize that you have to change the plans.
Why would I have to do that? They are not wasting time.
You just told me you're having them drive over an hour for nothing, that's wasting their time. Just be considerate and tell them the truth.