Bad idea but to each her own.
I was going to say chant too. To enhance the costume I would carry around a refillable mug and slurp it really loud and make a big mickey head ice cream on a stick she could carry as a prop
Then the post should be on the "just for fun" forum and not the "Theme Park" forum since it really has nothing to do with Disney vacationing. Perhaps that is why people are reading it incorrectly. Not to mention people do not call everything by the correct title, so I am sure the party title did not register with some of the members as a non-Disney event.
Sounds pretty stupid idea to me if everyone else is gonna be a villain why would you want to a be a rude guest.
Take this. View attachment 125980
If you take this idea to far, you will get to meet some Disney folks in white shirts. Shortly after that some in blue shirts to escort you from party. I don't think Disney will buy rude guest costume or behavior
Have her yell at a family with a wheelchair/special needs child about getting to skip the line and how "its not fair". I've seen posts on that before and I would go NUTS if I saw it in person. Luckily my Dad in wheelchair was treated really well.