My cousin's bachelor party was billed as "One Last Hurrah" on all the invitations, and we all made sure it lived up to that hype. He not only was getting married, he was also moving to another state and getting a huge promotion at work. He had a lot to celebrate, so it truly was the last hurrah for him as a young single man.
I agree with Inaventu that a last hurrah should be a significant and memorable occasional, but I'd also say it can be melancholic as well. We all enjoyed the bachelor party, but we also knew it was probably the last time all of us would be in the same room at the same time for a while. A last hurrah can sometimes require pulling up a few reserves of energy in order to send that person off with a true bang.