I'm a frequent rider of the DC Metro. When they built the system, they wanted it to be a pristine showcase for the nation's capital. (We'll overlook the fact that it's the most expensive subway system per mile in the US and that you have to pay for the privilege of not driving by parking at a Metro park & ride lot.)

So, since cleanliness is next to you-know-what, there are the usual no eating/drinking ordinances you'll find on most public transportation systems. But, to make the problem worse, they removed all or most of the public trash cans in the post 9-11 panic. Litter has increased dramatically, just because there's no place to throw stuff out. Also, there are no public restrooms in Metro stations. If you're really hurting, you can bow & scrape to the on-duty manager and they might consent to let you the employees' restroom. But, by then, it's too late or you've already gotten sick. ("You didn't throw up in front of Dean Wormer; you threw up ON Dean Wormer!) The stated rationale was, again, cleanliness. But, one could easily conclude that the hidden agenda was to not show the world that there were actual homeless people who used Metro restrooms in the capital of the richest nation on earth.

Since very little crime happens on the Metro, the biggest targets are the felonious eaters and drinkers and the slightest disagreement with a cop results in the incident described above. Folks that I've seen eating or drinking have generally been obvious tourists (Oops -- profiling!), and I've usually quietly spoken to them that the Metro cops get really weird about eating and drinking. Then, I block the line of sight between the tourists and the station managers until they have stashed their contraband.