Penguin #1 opening up Ringo's legs in the middle of her class; she immediately brings them back together, squishing him.
Ringo's strange musical fantasies from episode four.
Not only from episode four, the fantasies happen in almost all episodes she appears.
The penguins are this in spades, seriously - whether it's from #1 peeking under a waitress' dress or #3 dressing up in a wig, they're guaranteed to make you laugh at least once an episode.
Your mileage will vary regarding the penguins. A lot of what they do is either a blatant mood-killer (like #2's flatulence problems in the middle of a conversation), or just Dude, Not Funny! (like #1 stealing panties, or attempting to use a rectal thermometer on a nurse).
Episode 16's Survival Strategy has to be the best and most hilarious one so far. It starts with possessed!Himari holding up a sign saying "Survival Strategy!" and ends with her taking striptease pictures of Masako's maid Renjaku!
Lets not forget how she explains her intentions entirely in haiku, and Renjaku replies in (failed) haiku as well.
And then we have pretty much all of Esmeralda's interventions in that episode, specially when she tries to suffocate a small fire with a hose.
Both Masako's grandfather and father have pieces of paper covering their faces in the flashback.
The Gratuitous English is funny enough, but there's just something hilarious about the fact that it's surprisingly good English, as if they got an actual English-speaker for this one gag role.
Of the Survival Strategy exclamations, second place probably goes to the episode where the kids make takoyaki. Shouma and Kanba look up to see Himari, standing, and wearing the Princess of the Crystal Hat ... patiently finishing her mouthful before yelling her trademark "Survival Strategy!".
Episode 17's interaction of the penguins and a octopus.
Episode 22 starts with Hibari and Hikari attempting to make their way to Himari's house in rather overdone disguises... While still wearingthe scarves Himari made for them which they drew attention to on TV, and looking hilariously dorky while doing so.