"insert pony name here is best pony."
This simple term is used anywhere and any time a MLPFIM fan is enthused by a particular pony. These comments tend to appear most in forums, message boards, and Youtube video comments. Some situations:
-A pony does something impressive or amusing in the show.
-A fan's favorite pony merely appears and/or speaks in an episode (Derpy Hooves is the best example).
-A pony displays an unusual tendency and wins the approval of a viewer (for example, the normally timid Fluttershy appears to beat the shit out of a bear).
-A fan simply prefers one pony to all others and wants to make it known.
It is up to the individual fan to decide which pony is best, as the statement is highly personal, but some ponies (usually Fluttershy and Rainbow Dash) are labeled as best more often than others. Also, this term is not always absolute, as some will use it to merely display an increase in the approval of a pony, and will thus apply it to multiple fillies and colts.
Mike: Well Princess Luna returned and could not stop yelling when she tried to talk. Eventually Fluttershy helped her and...
Aaron: FLUTTERSHY IS BEST PONY.