HuniePop/YMMV

Crosses the Line Twice: Aiko's presents all being Japanese paraphernalia, with one of Aiko's reactions being "You're so racist!" in a fit of laughter.
Game Breaker: Using these date gifts: Suede Ankle Booties, Pink Mary Janes, Compact Mirror, Sunflower, Stuffed Whale and Pearl Necklace. This can get you through pretty much any date in the game comfortably. Of course you have to get the items first, but the earlier dates are easy enough to do without the combo.
Mexicans Love Speedy Gonzales: Nikki isn't the most flattering depiction of a typical gamer (hot bod and pretty face aside). There are also a number of typical gamers (like TotalBiscuit) that find her one of the more loveable heroines.
Narm: A good portion of the dialogue, especially from Kyu and Audrey. Kyu's introductory lines early on really set the tone for the game.
Narm Charm: Then again, the dialogue is also commonly cited as a reason for the game's popularity. It helps that only some of the characters exhibit a large amount of cheesy dialogue, while characters like Nikki and Beli are more downplayed.
Periphery Demographic: Because of the game's puzzle elements, it has developed a surprising number of straight female fans, though it is not uncommon for Dating Sims to have a female Periphery Demographic.
Strawman Has a Point: Audrey is right about Nikki needing to get out more. Bringing an introvert to a loud and busy nightclub was a horrible idea, but Audrey's concerns about Nikki being stuck in her room all the time are pretty sound. Considering Nikki's lack of social skills become less apparent after opening up to you, it looks like getting out there did Nikki some good.