That is very close to what I was thinking: Thunderhooves and Celestia are having a series of meetings regarding... something boring. Some banal dispute regarding apple trade rights. Thunderhooves is being stubborn, and even Celestias divine patience is wearing thin. She wants one of the Mane 6 in the meeting to help out. They've met Thunderhooves, his tribe, seen his lands, that sort of thing. Fluttershy was the last EoH to say "not it!", by virtue of not having said it at all. And yes, this meeting is so boring even Twilight thinks it's a total snoozefest.
Gustave has been hired by Celestia to handle catering, and is being "helped" by Pinkie, who hired herself. He goes up to the conference room carrying a large cake for tea. When he sets it down on the table, IT VIOLENTLY EXPLODES, covering all four in cream, strawberries and chocolate sauce. Pinkie's idea of livening the proceedings, no doubt. The next step is logical: obviously the best way to clean up the mess is for them to lick each other clean, one thing leads to another and fade to black, credits roll, thunderous booing from the crowd.
That was much shorter in my head. It sorta... kept stretching out. I'll have to be careful or next thing I know I'll be writing full-blown fanfics.