Another one: Mio finally giving in to Sawa-chan's hobby.
Season 2, Episode 14 — In an attempt to get hit in the forehead, Mugi tries stealing the one strawberry atop Mio's slice of cake. Just... watch. (S2 14 19:02)
Several moments in episode 18 of season 2, as if the plot for that — Mio and Ritsu trying to play against type — wasn't enough.
Mio's Freak Out in the beginning, complete with her listing reasons she can't be in the play that get more outlandish with each one, is pretty funny- and then the camera angle changes, revealing that Yui has been holding her arms like a tree the entire time.
Mugi suggests to Mio that she should pretend Ritsu is the only one watching her. Mio looks out at the girls and imagines that they all have Ritsu's face.
"That'd get noisy real fast..."
The show starts of hilariously with the first episode of the first season, when the girls try to convince Yui to join their club. In no time the club room changes into nothing less than a war zone, complete with emotional close-ups of all involved. That scene's punch line ("You guys are really not that great") is very funny as well.
There was also that scene a dozen minutes prior to that when Ritsu asked if The Promise Mio made was a lie. Her response? "That entire flashback is a lie"
And from the same episode, Azusa sounding like all four of her seniors on her way to the club room.
Omochi Race. That is all.
"WAA WA WA"
Azusa imagining herself as club president.
Nodoka stopping Yui from eating a crayon on the first day they met.
Season 1 episode 3. PUNI PUNI!!!.
The whole affair with Yui cutting her bangs. Without a mirror.
The whole exchange between Yui and college K-On member Akira.
On the first day of their senior year, Ui decides change her hairstyle...to look exactly like Yui. She then plays up the joke by saying that she really is Yui ("I wanted to see Azu-nyan and came here pretending to be Ui!")...and Azusa starts believing her.