Well done story. Mary befriends Joanna (Mary Frann) who rear ended her car. Joanna and Mary seem to socialise a lot and Rhoda feels discarded. (Joanna also seems to conveniently keep forgetting to pay for the damage to Mary's car, so we know something is up from the start... also, Phyllis likes her.) When Mary tries to include Rhoda, Joanna's anti-semitic beliefs are revealed.
According to a trivia item on this site the producers said in interviews that this was "one of the worst" episodes and that "everyone involved in the episode agreed it fell flat and was tonally way off-key for the series."
Actually the story is well crafted and well played. It isn't really off-key either. Not super heavy on laughs and crazy comedy, but a good story. Mary's bit when she confronts Joanna is very well done. Far from the worst episode of the series.