A [b]lack screenwriter is blaming an "old white lady" for getting him kicked off a train ... he says he was racially profiled, but cops in New York say he refused to take his feet off a seat. Alex O'Keefe, who writes for the FX hit "The Bear," posted video of himself being confronted by MTA police officers while on a train from NYC to Connecticut ... and he says a "Karen" complained and told him "to correct how I was sitting."