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: Viva Piņata
Animation Age Ghetto: Main reason why the game is so off-putting. It's too hard for kids, and too childish for adults.
Broken Base: The TV show fandom and the game fandom. Yes, they exist.
Demonic Spiders: Sour Crowlas are normally benign compared to other sours. However, if one comes into your garden and you have a sick pinata in there at the same time, smash it or scare it away fast. Their effectively mini versions of Dastardos when this happens. This tropper lost some of favorite pinatas to them.
Professor Pester will show up in your garden from time to time for the sole purpose of smashing your most prized Piņata. In the original, there's no way to stop the bastard once he shows up, and the only thing that will actually keep him out comes into play too late for the player not to have put up with him at least once. However, the DS sequel gives you a "Dastardos Shovel" that lets you stop him somewhat.
There actually is a way to stop him - and at the same time, the Ruffians - from entering your garden. Once you reach a certain level, you can buy the item 'Captain's Cutlass' from Costalot's store. It's a little pricey, but as long as it's in your garden, you don't have to worry about him. The same applies for Dastardos, as buying the Mumbo Jumbo statue will keep him out should one of your Piņatas get ill.
Buying decoy Piņatas, available much earlier than the Captain's Cutlass, will distract Professor Pester. You'll have to buy a new one afterward, but it beats losing a rare Piņata. Or you can just bribe him (which is cheaper than the decoy, but requires you to get to him fast.)
Fridge Horror: Some Ruffians have brown-colored tattoos on their hands and feet. At first they seem to simply add to their nastiness, until you realize what Ruffians probably do to captured piņatas filled with chocolate.
Pigxies are the sworn enemies of Rashberries and Swananas. This could suggest they're horrified of what they have created.
Game Breaker: The Wishing Well in Trouble In Paradise. Throw in 1000 Chocolate Coins, and you're pretty much guaranteed to receive several coins worth 2500 Each in return. Did I mention that the value of these coins can be increased by Five times just by placing a cheap item in your garden?
Goddamned Bats: Some of the Sours are a real pain in the ass, and they'll keep coming back until you're able to tame one.
If there's a certain pinata species you really like, or find useful—and that species happens to be part of the predation list for another pinata—you will probably be doing a lot of manual exterminating to keep your residents safe. This is possible if you just happen to enjoy having a certain species around, but for certain members of the mentioned "utility" species, it can get bad. This also includes incidences where one species doesn't eat another, but they do fight—things like Raisants and Buzzlegums, or Cinnamonkeys and Bonboons.
This is fixed in the sequel, where you can set the Bouncer Board at the corner of the garden to repel a given pinata from showing up at all. But only if you've already got the Master Romancer award for it.
Jerkass Woobie: Dastardos in the gameverse. Sure, he's a jerk who kills sick pinatas, but he was taken from his family against his will and turned into a husk of his former self by Professor Pester. Not to mention no one knows who he actually is, so he'll probably be estranged from his family forever...
How has no one mentioned Langston, yet? After episodes like "My Pal Langston" and "Langston's Jameleon Cousins", this troper can't help feel like he should qualify too.
Les Yay: Leafos supposedly wrote the descriptions in the Journal, yet one of the entries talks about kissing a girl...
Mercy Kill: Woe be to you if a piņata falls ill early in the game, when you can't afford the doctor and you haven't unlocked the chewnicorn. This may be the only option if you don't want Dastardos to show up.
Squick: The game doesn't keep track of families, so not only is Brother-Sister Incest a possibility, but you can even mate Piņatas with their own parents or children. To be honest, there's so much inherently wrong with the game that there's even a VGCatscomic that sums it all up nicely.