Swearing by youth, in its intoxication, youth itself has been subjected to injustice.

This couplet speaks about the ironic nature of youth. It suggests that in the very pride and exuberance of being young, one can sometimes unknowingly commit injustice upon their own youth. It's like saying, 'Swearing by youth itself, in the arrogance that comes with being young, youth has ended up harming or doing wrong to itself.' This could mean squandering opportunities, making hasty decisions, or engaging in excesses that ultimately diminish the true potential or beauty of one's youthful years. It highlights how the very strength and confidence of youth can, if unchecked, lead to self-destructive actions.