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: MLP: Friendship Is Magic S2 E7 "May the Best Pet Win!"
Broken Base: Whether or not Rainbow Dash putting the animals through so much danger was fine, even if they were willing. Oddly, a lot of people that feel Rainbow Dash was a jerk for doing so seem to forget or ignore that Fluttershy was just fine with the contest too, even exuberant about it.
In addition, there is a little known Dash fic wherein Rainbow adopts and trains a falcon. Sure enough, a falcon is one of the contestants and even appeared to be the winner. Coincidence? Yes, definitely, but no less hilarious either way.
Jerkass Woobie: Let's not sugarcoat it. Rainbow Dash's behaviour in this episode was very similar to the hare in The Tortoise and the Hare only caring about speed, brushing Tank off, and she's a Drill Sergeant Nasty, but at the end of the episode, when her wing is trapped under a boulder, you can't help but feel sorry for her.
Mondegreen: "There are falcons and eagles / They are both quite legal!" Sorry, "regal!"
Narm: Spike's shout of "Rainbow!" Especially since it's the first time he speaks in the whole episode.
Rainbow Dash's amalgam of the other Mane cast's pets looks so silly and harml—OH MY CELESTIA!
Rainbow gets her wing stuck under a boulder, without any chance of help arriving any time soon. Similarities to 127 Hours have not gone unnoticed All her friends knew exactly where she went and she was within easy binocular range, so she was probably being a little overdramatic.
The Quarry Eels. While the scene was played for laughs, Rainbow Dash's lack of consideration for the animals' safety doesn't come off well when the bat nearly gets eaten, and the eagle briefly looks like its head was bitten off, You could argue that this is why only those animals participated in the race (the tortoise wasn't invited but joined anyway). All the different animals participated in the other contests, so there's no evidence that any sort of elimination was going on. Maybe for the final event Rainbow only included the ones she knew could handle it (hence why the butterfly doesn't join, even though it "won" an event).
Painful Rhyme: More like not a rhyme at all - while the song is generally pretty good with its rhymes, one stanza near the very end of the song sticks out like a sore thumb.
Rainbow Dash: The bat would be awesome, but the wasp I'm digging too D'you have something in a yellow striped bat? Fluttershy:No, I've got a hot pink flamingo, just dying to meet you! Rainbow Dash: What to do, what to do?
The "fixed" versions, while slightly improved. From the side, you'd be able to see the pony's lower jaw extending downwards and the smile curving up around her snout, but from the front it's just a smiley face with a mouth curve that changes shape.
Wangst: Rainbow Dash carries on about being trapped forever, despite her friends expecting her at the finish line very shortly and knowing exactly where to look for her, and two of them easily being able to magic the boulder off her wing. She was probably just giving in to panic for a bit.