I told the check-in assistant at the airport to send my bags to New York, while I flew to London...

 I told the check-in assistant at the airport to send my bags to New York, while I flew to London. She said she couldn't do that. I replied, ''why not? You did last week!''

This airplane joke is funny because it involves misfortune, and also a misunderstanding. The idea that the jokester had his bags delivered to the wrong airport makes everyone listening to the joke feel sorry for the jokester, which is funny. The misunderstanding that the jokester is laboring under is that the airport could do that intentionally, and that it would be possible to order that it happens. The fact that he misunderstands this is funny. It is also possible that his last statement is an insult - calling the assistant a liar, which would make it funny because it is rude as well.