I pointed out that everyone knew you had to have more than 6 months on your passport to leave the EU - he said this wasn't common knowledge
It's not common knowledge, because it's not true. None of the none EU countries picked at random from the foreign office website that people regularly holiday in require passport validity beyond the end of the trip.
Canada
Cuba
Dominican Republic (as a tourist)
Mexico
USA
Most useful piece of advice is that you can renew your passport 9 months before the expiry date without losing any time. We did ours one January and they were back within a week. Saves the early summer panic when 'everyone' notices that their passport is about to expire and turnround times grow massively.
Its a good idea to keep a list of these things. As well as passports, there's EHICs, driving licence photocards, car tax, insurance, MOT, house insurance, all very important and easy to forget if you don't keep on top of things. I have a spreadsheet with a to do list in that I look at once a month on payday when I check our bank accounts and credit cards. Other people use various phone calendars and apps.
Not the most exciting thing to do, but part of being an adult and the consequences of not keeping on top of things can be anything from annoying to quite devastating if your house insurance runs out and you have a fire, for example, or you lose your holiday because your passport has expired.