"My name is Gregory Goyle and I smell." Written next to the entry on trolls for bonus points.
The book's intro talks about how wizardkind sought to differentiate between "beings" and "beasts", with the first classification of a "being" being anything that walks on two legs. This subsequently leads to chaos at a meeting of all these "beings": trolls smash the place up, hags look for children to eat, and Augureys make a huge din. Ultimately, the wizard in charge of opening the meeting runs cursing from the hall after slipping on some Porlock dung.
This conversation scrawled on the first page:
Harry: This book belongs to Harry Potter.
Ron: Shared by Ron Weasley because his fell apart.
Hermione: Why don't you buy a new one then?
Ron: Write on your own book, Hermione.
Hermione: You bought all those Dungbombs on Saturday, you could have bought a new book instead.
Ron: Dungbombs rule.
And of course Janus Thickey's "last words", a scribbled note saying:
"Oh no, a Lethifold's got me, I'm suffocating"
And later it turned out that he was actually having an affair with a local barmaid. Naturally, his wife was not pleased.