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.
Designated Protagonist Syndrome: Inverted with Tadakuni. He's a plain Generic Guy with no backstory and has less relationships with other characters than his two friends Hidenori and Yoshitake. Tadakuni's suffers from being Out of Focus, with basically no presence in some episodes and many chapters. His status is often lampshaded. However, Tadakuni is one of the most popular characters in the series and he's much more popular than Hidenori and Yoshitake. He's Out of Focus after the first volume and episode 5, making him somewhat like an Ensemble Dark Horse.
Ensemble Darkhorse: Karasawa, the Literature Girl, Ringo-chan, Habara/Archdemon and NAGO. Several popularity polls in, and Karasawa and Habara in particular seem to have permanently occupied some of the top places ◊, coming in (as of the March 2012 poll ◊) in 1st and 2nd place, respectively.
Given Tadakuni has been seriously Out of Focus after the first volume of manga and the fifth episode of anime, his position in the polls—far beyond Hidenori and Yoshitake—also makes him one.
Friendly Fandoms: The relationship between this show's fandom and Nichijou's fandom, both due to them being similar in name and due to them sharing a genre. Both will argue about which show they think is better, but the arguments never get heated, and both fandoms seem to respect each other and their respective shows. If someone has only seen one show and not the other, fans will often urge them to watch the other as well.
Shipping: If after the author's comment that the series is strictly a comedy with No Hugging and No Kissing, you'd expect that something like this wouldn't happen, you thought wrong. Indeed, there are several fan-favorites just from the anime alone, including but not limited to:
Hilariously all the pairings listed above (save for Karasawa) were featured in the episode 12 skit High School Boys and ... only to be sunk quicker than the Titanic due to the skit itself being All Just a Dream.
As homosexual ships are concerned:
All possible seme/uke combinations of the main trio are being shipped. Of course, since Tadakuni is an Attractive Bent-Gender, he's more likely to be the uke.
Motoharu and Karasawa
alternative title(s): Danshi Koukousei No Nichijou