Will second all of the Tom Sharpe books. Riotous Assembly was his first book. It git him deported from South Africa. The sequel to it is called Indecent Exposure and is also very funny. I would also recommend the Wilt books by the same author. They are (loosely) based on his job as a Polytechnic lecturer (remember them?) after he moved to the UK. Also worth reading by Tom Sharpe are Vintage Stuff (about a psychopathic schoolboy who takes everything literally) and Ancestral Vices.
I’ll also second all the Spike Milligan war memoirs. Very funny and also very hunbling.
Have a crack at the Flashman books by the late, great George Macdonald Fraser. They are the fictional memoirs of Harry Flashman VC, KCB, KCIE, Briatin’s greatest war hero who is at the heart of every major military and political escapade from 1840 until 1904 (incl The Afhgan War, The Indian Mutiny, The Slave Trade, Custer’s last stand, The Charge of the Light Brigade, The Zulu War et al) despite his increasingly desperate attempts to leg it and/or surrender. In truth he’s a coward, a shsyter, a cad and a layabout, yet he always manages to emerge from the most heinous situations with his credit intact and his reputation enhanced. In truth it his natural skills at languages and disguise, horsemanship and womanising – few women can resist his manly charms and more often than not the Flashman gambit (left hand on breast, right hand on buttock and go for the lips) does the trick – that get him out of trouble! The books are extremely well written, very funny and also remarkably historically accurate (other than Flashman of course, who didn’t exist). There’s a reason that none of them have ever been out of print since the first was published in the early 70s. Enjoy!