In season 6 episode 22 called "PPOV" Pinkie AJ and Rarity take a boat trip together and end up fighting, then a storm comes causing their boat to capsize. Twilight tries to figure out what really happened since the girls blame each other for the capsizing, but each pony she talks to gives a different story. 

So here's what I think actually happened during the trip, enjoy.

End music: Independent Together Instrumental from Steven Universe Movie

And if AJ had also said "it all started at the docks" it would have been perfect xD