How should I ask my boss for vacation leave last minute?

As a boss, the one thing I can't stand from employees is lying and "excuses". The way you worded your question is exactly what I'd go to the boss with. Most bosses have lives outside of work, too, so they might actually understand. They will just want assurance that this won't happen frequently. One of my employees came to me recently with the same kind of thing- someone had dropped out of a tour group to Italy and she had to respond that day. She told me she felt very badly especially since we're so busy, but offered to make sure everything would be taken care of and that she'd work the first day after returning. She also said she understood if I said no (not sure I recommend that). I told her I thought she was crazy if she did not take this opportunity. She went, she followed through on all her promises, and we're both happy. Bring back pictures, and show them around at work. If they say no, you will be in a tough spot and have to decide whether to stay or quit (I'd quit).

I suppose you might as well tell the truth. They probably won't believe you anyway, unless it's a good one. Then again, do they deserve the truth, not personally, but the company? Going to Honk Kong seems like a once in a life opportunity. Maybe you can offer to show them the ticket, if you get an OK. Then again, what job is worth passing that one up. I'd quit and stay longer or alternatively I'll go. LOL

Tell him the truth. Why make up a story?