I started to fit the brompton rear light onto dearly_beloved's bike, which I realised has been sat in the dining room festering in a fair-to-middling coating of mud and road salt from him having gone out in the snow just before Christmas. It was absolutely minging, and the chain was completely dry and somewhat rusty
He's had it for 2 months and never even oiled the chain.
So... I just cleaned dearly_beloved's bike. It's quite tricky to get a bike upside-down in our kitchen - since it is the width of the bars plus about 4". On the bright side, it means that there's not much filthy floor to clean. And I liked somebody's top tip from here of using baby wipes to clean your bike
Slightly less good is that he obviously didn't even wipe the chain on littly's bike either when that came in at the same time - and it's as gruesomely filthy, although minus the rust. Guess what I'm going to be doing... tomorrow.