Hyouka (2012) - S01E06 - To Commit a Grave Sin
Committing a Cardinal Sin
One day, while Houtarou is in class, the class is interrupted by a commotion at another room down the hall. After his class is finished, he spends the rest of the afternoon like he usually does at the Classic Literature Club. But this time, at the club room, Mayaka is angrily reprimanding Satoshi for having missed what sounds like a date. The four club members then diverge into a philosophical and social discussion of what it means to be angry and the relevance of the Seven Deadly Sins to society and human beings. Having heard Eru's voice during the class commotion previously, Houtarou remembers the event, and asks Eru what the commotion was about and why she got angry during the commotion. Houtarou later figures out that the commotion was due to the class's teacher's misunderstanding, but neither Houtarou nor Eru can figure out why Eru got angry during the commotion.
(Source: Wikipedia)