Best Customs story I can come up with is leaving my hand baggage next to the carousel after claiming the heavy bags when coming home from deployment into BWI. Because I left the baggage area and came out into the non-sterile area, that qualifies as the dumbest thing I ever did travel-wise. Customs agents were kind enough to rescue my backpack after flashing my ID. Close in second place is when my mother gave me a card to mail from the airport in FLL - envelope in one hand, paper ticket in the other...I was so ridiculously tired that I had the ticket pushed almost all the way into the mail slot before I realized that it was the wrong item.