This expression has been used in the trilogy a total of 16 times. In Part I, 1955 Doc says it on three occasions. In Part II, 1985 Doc says it on five occasions, while 1955 Doc says it once. In Part III, 1955 Doc says it on three occasions, while 1985 Doc (now in 1885) says it on two occasions. Finally, Marty uses the expression, in a humorous reversal of roles.