My point is that the "piss in the car" comment was mean, thoughtless, and added nothing. If grandpa is incontinent, then he'll wear diapers regardless of the car or the bus.

Your comment was either a.) implying that messing themselves in public was better than in relative privacy, or b.) if you use a car, grandpa doesn't get to wear Depends.

Take your pick.

It might not be what you meant, but you were too busy being a jerk to notice that it's what you said.