I got one that I really should have contested but I simply paid anyway. It was in the days when, as well as double and single yellow lines, there were also dashed (broken) yellow lines to indicate parking restrictions only applied at limited times. I was looking for a parking space outside an auction site in Norfolk and spotted a nice big gap, which I could easily get my car into. As I got out of my car I looked to check that I'd not inadvertently parked on any yellow lines; I hadn't. However I returned to find I'd got a parking ticket because the yellow dashes on the road had actually been marked so far apart that one started by the front wheels of the car ahead of me and the next was by the rear wheels of the car behind me but my (completely non-yellow-lined) bit in the middle was still covered by the parking regulation! Grrrr!
Other than that, I've had just one ticket for overstaying on a Pay-&-Display car park after becoming engrossed in a secondhand book shop for far too long.
I've also had to pay an 'after hours release fee', from a car park in Stratford, after I'd been stuck on a failed Central Line train for ages, preventing me from getting back to the car park before it closed.