"Concentration" is a piece from the background score that is absolutely wonderful and it's used whenever Bossun is in "Concentration Mode". That is partially due to the fact that the animation wouldn't work if Bossun was just sitting in there thinking and connecting points he missed at simple sight. In-Universe, his "Concentration Mode" is boring and uninteresting for his peers.
"Cool & Crazy", when stuff is going in favor of the Sket Dan.
Any song played by The Sketchbook that was used in the anime. Especially "Clear" (the last opening of the anime), since it pumps you out.
Die for Our Ship: Initial reaction from the fandom towards Saaya Agata was bad (she is a parody to the Tsundere character archetype, for starters), but it got worse when she developed a crush on Bossun, the Oblivious to Love hero who wouldn't notice that Himeko also had a crush on him (whose relationship was beyond "Like an Old Married Couple" status). Saaya later confesses her feelings to Bossun (and she hints them to Himeko beforehand as well, due to the School Trip Rhapsody arc's circumstances), and she eventually gives up when she finds out that he gives a "special" attention to Himeko that he can't notice besides their friendship.
Ensemble Dark Horse: Several non-characters are so popular they ranked well in the popularity polls, which gets lampshaded in the popularity poll chapters when the characters are flabbergasted to learn about how popular they are. These include:
Surprisingly, Switch's Bossun drawing, a non-character that has its own popularity inside the series, which was ranked 5th (aka after the main trio and more popular than Tsubaki and Agata) in the first Popularity Poll.
Anthony (an action figure from "Slender", a tokusatsu-parody show) — he got 13th (Bossun was only expecting him to be about 75th).
Tanabe-kun (a "character" that was created by Bossun and Tsubaki in their attempt at fixing the writings in a banner), which got placed 22nd aka the same as Shinzou.
Friendly Fandoms: With Gintama (although it borderlines into Fandom Rivalry). Both series have been constantly compared on and off from time to time ever since Sket Dance was first published, due to their similar premises (resolving problems through an Odd-Jobs Shop) and comedy (Boke and Tsukkomi Routine, Breaking the Fourth Wall, etc.), especially since Kenta Shinohara may have been inspired by Gintama at the time he was working as an assistant to Hideaki Sorachi. However, both series play off each other's weaknesses and strengths in their own styles, according to their narrative storylines and characters' relationships.
Harsher in Hindsight: Switch's Large Ham personality is a way to show off his emotions to his friends and other strangers as well, and to make him look normal, although he speaks through his laptop. Until it is mentioned in "Switch On" that he developed it (and his pop culture references' knowledge) when he was a shut-in, as a way to maintain his mind busy at the time he was still mourning the loss of his younger brother.
Soujirou Agata and Michiru Shinba's relationship. They have been best friends since they started high school, and Shinba often worries about Agata's well-being when he focuses his attention into an obsession, such as that time he thinks there was a Love Dodecahedron involving his little sister, Saaya. The anime, in fact, ship teases them a lot as it uses scenes that are nonexistent in the original manga.
The Undying Loyalty that Kiri develops towards Tsubaki sometimes goes into exaggerated extremes — he agrees with him in anything he proposes, and he has saved his own butt a couple of times. Eventually, Tsubaki gets used to it.
Switch's loyalty towards Bossun is meant to be platonic but can be easily interpreted as otherwise.
When looking back at how they become acquainted with one another, Switch initially romanticizes how Bossun "reached his hand" through his room's window to save him in the past.
Whenever Switch says something really smart, Bossun keeps screaming "I love you!" and how he just wants to hug him. The best part is that Switch always tells him to go for it.
Incest Yay Shipping: Despite their twin reveal and the No Yay that ensued, Bossun/Tsubaki still has its slash fans.
Obaanyan, a character created for the Sket Dan's reimagined version of Momotarō, thanks to Switch's suggestion of changing the old foster mother of the protagonist to someone younger, who happens to be half cat.
Koma-chan, who despite being a tall girl seen as a "giant" by her classmates, is incredibly shy and some of her poses in some scenes are a little suggestive to highlight her "moe-ness".
No Yay: The idea of shipping Bossun/Tsubaki is understandably offputting to many fans due to their eventual twin reveal.
Platonic Writing, Romantic Reading: A chapter in the series, "Brother and Sister", explores the ambiguous ties between Bossun's not-blood sister, Rumi, and his biological twin brother (who had been separated at birth), Tsubaki. They are supposed to see each other as siblings, but the way their relationship develops follows the exact same beats of a romance arc: First, Rumi gets offended when Tsubaki tells Bossun that he doesn't see her as a sister the same way a love-struck girl might get upset if she overhears her crush saying that he doesn't like her that way; Bossun then tries to rectify this by having them spend some alone time together—which looks suspiciously like a date—and the day ends with Tsubaki saving Rumi from falling off a bunch of stairs, after which their relationship improves vastly.
The mascots from "Can Mommy Come Too?", a show where Remi Onee-san was its host, have their charm. In-Universe, kids simply adore them despite their appearances.
" (the last opening of the anime), since it pumps you out.