Another vote for Adrian Mole - I remember laughing a lot at the bit where he came home unexpectedly early from school to find his dad watching Playschool and pretending to be an acorn growing into a tree. I was lucky enough to be in a stage version of the musical of The Secret Diary of... (aged up considerably to play Grandma Mole) and that was funny too. I also laughed aloud at one of Sue Townsend's other books, The Queen and I.
I've also laughed at bits in Jane Austen, the Famous Five, and "Jill's Riding Club" (I had quite a lonely and unhappy childhood, perhaps that explains it), and involuntarily gasped out loud while reading a Harry Potter book on the bus once, much to the amusement of my fellow-travellers.
I'm no "screamer in the Sistine Chapel" by any means, but I was fortunate enough to find myself on the Harry Potter Leavesden Studios Tour a few days ago. Not so much laughter, but I let fly a very loud expletive in the Forbidden Forest bit when the bl~~dy giant spiders unexpectedly descended from above. Fortunately there were no little children in the vicinity.
Time and a place though - I've been to a few RSC things; memorably a performance of Richard II (very definitely NOT a comedy) and there was a lady in the audience loudly fake-performance-laughing to anything she perceived to be mildly witty in order to telegraph her higher intelligence to the rest of us plebs. It was visibly annoying the poor s~ds in the cast. I do prefer to keep myself to myself, especially when reading, but sometimes a chuckle comes out before I can censor or stifle it.
Some of us are just more outwardly expressive than others, I guess. It doesn't mean that you don't enjoy and delight in books as much as other people @Sidebeforeself - you just love them in your own way, and that's brilliant.