People-watching is probably the best on the T in Boston. mmm, I love Boston.

Everyone uses the T.
Very attractive, artsy young men travel on the T.
Successful business women dressed in a black skirt and skin-colored fishnets rests on the T.
Old, Mr. Potato Head looking men who wear enormous black rimmed glasses and talk themselves since no one else is listening when the subway is momentarily delayed, hurries through the T.
Young love traverse the T.
Sketchy tough guys take the T.
And so do many many drunk people on New Year's Eve.

Really, it gets quite interesting to relax and see diversity sitting beside you.