1) This happened a year or 2 ago: a Caltrain passenger/cyclist told me I had to fold up my bike instead of parking it in the bike car like every other cyclist do, so that a space could be "saved" for other cyclist with non-foldable bikes. The intention was good but where am I supposed to put my folded bike? Caltrain's rule says that folded bike should be put under the seat (which is not possible for mine or most other reasonably sized bikes) or on luggage rack (which is 3 cars down. Dragging my bike through 3 cars was a workout that I didn't need) so I declined and that dude wanted to continue to argue with me but stopped by other fellow passengers. I didn't say another word and problem solved.
2) This happened today: instead of asked by a passenger, I was asked by a Caltrain conductor to do the same. To make things worse, this time another passenger (a 架兩) actually chimed in to support the conductor! I explained the problem again. And the conductor gave me permission to violate the aforementioned rule: she told me to put my bike on the seat! (And allowed me to seat in another one) Well, how was I supposed to refuse such a good offer? Since the aisle is too narrow for me to push my bike thru, I have to pull it off the ground and carry all the way to the empty seat in the back of the car. And this was the by-product:

Oh yeah, I told the 架兩 it's none of his business.
[Update: the bike chain grease stain on my pants were safely removed by Shout (Triple Action Stain Remover)]