I took the tram to go to school for 10 years and have maybe a handful of weird incidents to show for it. This is an issue with the culture surrounding public transit. If it gets seen as the mode of transportation which only gets used by those icky poor people and weirdoes it is no wonder that the weirdoes are overrepresented, especially in the US where the only place with a tram system of note is NYC which already has a high amount of weird people living in it, even if only due to the huge number of people living there to begin with.