There are few things that will persuade Ritsu to lift her head from a book, but it seems like two of the other residents engaging in an attempted assault is one of them.
The spark for all of this is a party which led to Sayaka running into an ex-boyfriend, the frustrations of which she now seems keen to take out on Mayumi for whatever reason. Still, it's nothing that a plastic bag over the head can't resolve, and once everyone has suitably calmed down discussion somehow eventually turns into comparing relationships to computer file systems. There's probably a joke I could make here, but it's a bank holiday so I've got nothing...
From here, a hot day finds Ritsu in surprisingly high spirits, enjoying a good old fashioned water fight with the others thanks to some recently discovered water pistols to pass the time and cool everybody down. Inevitably, the source of her mirth and good humour comes from the book that she's been reading, and when Usa spots said book lying around just begging to be read he spies an opportunity. Caught reading the book by Ritsu gives him an unusual chace to talk literature with her that she revels in - something which ultimately continues even after she overhears Mayumi suggesting that his reason for this share loved of the book in question is far from pure. The trouble is, nobody's tastes overlap perfectly, and this soon becomes clear as his reading progresses... although Ritsu doesn't seem to mind one bit, Usa is devastated at what he seems as a mortal blow to his progress with her.
When it doesn't get stuck in a rut upon relying on the same veins of humour repeatedly (there are only so many times jokes aimed at Mayumi and Sayaka's relationships you can take before they stop being funny), The Kawai Complex Guide to Manors and Hostel Behaviour continues to be a pretty fun show - if nothing else, watching Ritsu's reactions (or lack thereof) to everything seems to be ceaselessly entertaining, while also providing the series with some backbone in terms of continuity and development that stops it from being "just another sitcom". It's no comedy classic, but it hits the mark just often enough to be successful, and that's really all I can ask of it at this juncture.