"Mexican jumping car" is what I call those lowriders with the hydraulic systems that enable a vehicle to bounce up and down.
Perhaps it's a bit of an ethnic slur, perhaps not. In any case it never fails to get a laugh, due to the instant word-association with the Mexican jumping bean, and the fact that, more often that not (where I live anyway), someone of obviously Hispanic descent is at the wheel of whatever hopping-mad Spud Webb of a vehicle is being admired.