"Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind."

Apparently this quotation is often misattributed to Dr. Seuss, as described in wikipedia.
Bernard Baruch in response to a question by Igor Cassini as to how he handled the seating arrangements at his dinner parties, as quoted in Shake Well Before Using: A New Collection of Impressions and Anecdotes Mostly Humorous (1948) by Bennett Cerf, p. 249; the full response was "I never bother about that. Those who matter don't mind, and those who mind don't matter." This anecdote is also quoted online at Chiasmus.com. It has also become part of a larger expression, which has been commonly attributed to Dr. Seuss, even in print, but without citation of a specific work: "Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind."
From
http://en.wikipedia.org/wiki/Bennett_Cerf