I love the use of the F word in entirely different ways,At the reunion, Ennis uses it as a positive reaffirmation,In their last trip, Jack uses it or a version of it,as a complete opposite, it is a desperate almost throwing in the towel.
So just one word, used albeit in 2 slightly different forms by Jack and Ennis, serves to underline the ongoing conflict between the two.It is interesting that in these instances, the use by Ennis is optimistic, whereas Jack's use is quite the reverse.
It is an example of the role reversal that occasionally occurs with the two.