These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: The Life And Times Of A Winning Pony
Nightmare Fuel: Rainbow Dash getting increasingly aggressive and incoherent after receiving one blow on the head too many.
Unfortunate Implications: Things do not bode well for the future of the Y-Chromosome in Equestria. Because mares can conceive through "The Magic of Love," entire family trees consist of mares (though according to Word of God it is also possible for stallions). The ratio of stallions to mares is already severely skewed in favor of the latter, with indicators that the discrepancy is only going to get worse as time goes on.
What an Idiot: As a filly, Rainbow Dash is incredibly bullheaded, to the point where she seems actively opposed to having an actual plan for anything. In the present day, she's only gotten a little better, with most of her plans boiling down to "Throw myself into the thick of things with no forethought, then make the impossible happen." The fact that she's still alive, let alone still has a job, is a testament to her skill and raw charisma as a leader.
Derpy: “Rainbow, you idiot. You jumped into a cloud without checking for lightning. Again.”
After an argument where Cloud Kicker calls Derpy too possessive when she expresses concern that Cloud might leaver her for Fluttershy, she kicks Derpy out because Fluttershy overheard it and cries, thinking she's driving a wedge in between them. Then Cloud Kicker gives into her impulses and has sex with Fluttershy, and afterwards desires to marry Fluttershy before anyone could object. It's hard to be too concerned when your marefriend does this once you leave.