Please excuse me while I wait for my sides to recover. Hilarity, pure unadulterated hilarity. Good drawing style, nice implications RD has narcolepsy? Sounds dangerous), and excellent punchline.
Speaking of implications: if Luna puts the stars that way because she's on a diet, and astronomers have since named the constellations after this position, that would mean Luna's been on a diet since before her banishment.
*takes away celestia's cake* okay, celestia, that is just fucking cruel, you are making a pony with a huge sweet tooth suffer through watching you eat cake while on a diet. and you're doing this to your own damn sister!!