I need short and interesting book (max 100 pages), preferably non-fiction. Give me your best recs.
If you're not deadset on nonfiction, you could try an anthology of fables/myths (I've been reading Aesop a few pages a day for weeks now), or the Arabian Nights, one story at a time.
For nonfiction, maybe Plutarch's Lives. Cumulatively they're long, but each life is only given 30-50ish pages.
In fiction, if you like horror movies, try The Hellbound Heart (Clive Barker). It's easy to digest the source material for the Hellraiser movies.
Also, there's an obscure little book that none of the other anons seem to know about. :^) It is called the "Tractatus Logico Philosophicus", by Ludwig Wittgenstein. But I would only really recommend it if you have some prior background in math/logic.
Are you in Australia? If so black publishing released a bunch of books this year (think they're titled 'short blacks') that are short essays by australian writers (helen garner, galurway yunupingu, john birmingham etc.), those are pretty good. Or you could pick up that 'best australian essays 2015 book. If you aren't australian, well who knows, you can go fuck yourself i guess.