Things that are hilarious to me:

• Rei said she didn’t think Usagi should go to the party because she had a bad feeling. But here she is, going to the party with Usagi. 
• Ami and Rei don’t have disguise pens, and the dialogue suggests they didn’t use Usagi’s. That means they had those tiaras. Or else went and bought them just for this.
• Usagi looks so demur and graceful in this cap, and nearly the whole time she’s in this disguise. She believes so much in the power of a costume.