Could it be that they are just 19 or 20 years old , and have not fully stepped into the shoes of experienced adult people like ourselves, who are trying to place rational reasons on all of their actions?? Speaking for myself, I did many things at that age that would now seem odd, or impetuous. I think men, especially under their circumstances and in 1963, might well do and say the things that they did. I think Ennis was hurt and confused, and I think Jack was using whatever familiar means he knew (lasso), to reach out and grab Ennis. It was a simple gesture, at first meant to say "I love you and want you to be with me" or, " Hey, its not so bad, we still have each other", and in the turmoil of youthful innocence, turned into the playful brawl of boys. Two men, very young, unable to cope with their feelings, expressing adult emotions, but not yet skilled. Many of us have been through this. I do not see the same hidden meanings in these scenes as others suggest. To me it is very simple. I feel what they feel. They express it as boys do. The simple emotion is still beautiful at this point of the movie. The shirts are a testament to the this youthful innocent bliss. One of the most powerful statements from beginning to end.