The latest “subway shmutz” report is out and the R train received a very nasty grade. According to the annual survey by the Straphangers Campaign, only 27% of R trains were deemed “clean,” making them the dirtiest in NYC’s transit system for the second year in a row. The 7 train on the other hand, was rated the cleanest at 68%. Other highlights: The M was most improved. The 6, B, E, L and R are getting worse and the 1, 2, 3, 4, 5, 7, A, C, D, F, G, J, N and Q trains remained “statistically unchanged.”