Kagami: What's with the (bleep) D-like driving!? note The "bleep" was intentional. It's part of the dialogue.
Or how about in the same episode when, after Tsukasa puts a seashell to her ear and imagines she's floating in the ocean, a roach pops out, prompting a very reasonable scream and making her run to her sister?
Another favorite is in the "Wawawawasuremono..." ending, which includes Shiraishi singing next to a random couple (who seem to be trying their best to ignore him), and a subtitle pops up pointing at them which reads: "Random couple who readily agreed to be in this video."
The New Years episode was memorable because out of the blue, Tsukasa says some odd dialogue ("Rice cake goes wee!" and "Cheesecake?").
After Konata's famous "a flat chest is a status symbol" scene, Tsukasa replies "I guess I'm safe too".
In episode 21, where they go to the Daibutsu in Nara, and Konata calls the figures around the main statue "the options".
Konata: Hmm... if this dude's the main one... then the little ones around him... are all the Options!
A blink-and-you'll-miss-it moment in the MMORPG part of the OVA: When Konata and co. do a team victory pose, a random male character joins in on the far right, and then just walks away without anyone noticing.
This troper can't contain any laughter whenever the scene comes on, right after Konata's trying to think of a good nickname for Kagami. Kagami, trying to get her to stop, trolls her with 'just call me Kagami-sama', or 'The Great Kagami', as it's subbed as. Cut to later that day when Konata visits Kagami's classroom, full of students, so that they can walk home.
Konata: (waving) Oi, Kagami-sama!
Kagami: (blue-faced) Oh my god, she actually said it!
Konata explains Kagami how she met Tsukasa: A foreigner (Who bears an intentionnally uncanny resemblance to Guile) was about to kidnap Tsukasa when Konata showed up and beat the crap out of him Street Fighter-style. Tsukasa corrected her by precising that the foreigner was actually asking her for directions.
Why hasn't mentioned the moment when Kagami, in the bread eating contest at their school's sports day, overcompensates by biting the bread and bringing the WHOLE RACK it was on crashing down? This troper couldn't breathe too well after watching that.
The concert had two, both from Minoru — dancing with a Nyamo plushie during "Ore no Wasuremono" and crossdressing as Miyuki in the last several minutes to make up for Aya Endo's absence (Tomokazu Seki even tries to flip his skirt during the curtain call!).
Watching the English subbed version as a non-Japanese speaker can pull a few laughs, with Japanese words sounding like English words (Cookiecookiecookiecookie), as well as the genuine Gratuitous English.