Raisin
Explanation
The Joke
A teacher is explaining raisins to a class, describing how making a raisin involves taking a big cake, noting that there are raisins inside, and that every raisin has a beginning part and an end part. A student asks "Nobody cares?" The teacher then says the students act like raisins are so many, but that is because they do not recognize that raisins just exist and end in particular regions of the cake.
Wait -- on closer reading, the teacher is actually explaining something confusing about a cake with raisins in it, going into increasingly convoluted detail about how each raisin has a beginning and an end, to a class of bored students. When the teacher asks "Are you bored? Do you understand now?", the student in the final panel says they are irritated at being confused about something they never cared about, and asks if they could have a longer break instead.
The comic is satirizing the experience of sitting through a lecture on a topic so obscure, convoluted, or poorly explained that the students cannot even muster the energy to be bored -- they are instead annoyed at having their time wasted on something incomprehensible and irrelevant. The teacher's earnest attempt to explain the topology of raisins in cake is a stand-in for any academic lecture that loses its audience completely.
The Humor
The humor comes from the perfect encapsulation of a universal school experience: a teacher passionately explaining something that is both confusing and utterly unimportant to the students. The final panel's distinction between being "bored" and being "irritated at being confused about something I never cared about" is a wonderfully specific articulation of a feeling most people have had but never quite put into words. The student's request for a longer break is the cherry on top -- they have completely given up on the educational content and just want the ordeal to end.