"Fixtures" was the name of the school diary which every boy was issued with. These would occasionally be lost or left behind, of course, and when you needed to look something up (e.g. dates of sports matches) you would, naturally enough, ask to borrow someone else's. And Freddie Messon-Gilpin would, naturally enough, lend you his in the middle of double biology. And you, sitting behind him, would proceed to draw enormous phalluses, complete with Jap's eye and cum-lines, all over it. If there was time, you could fill in all the space available for each day in the year, and he'd have to buy another one.
(Have you borrowed another person's book and filled in every available gap with cocks, spunk lines and women riding around in tanks with their tits out? We're starting a competition to find the most cock-saturated page of a standard exercise book. Tell Log if you think you've got Britain's most cocks on a page.