When your colleagues no longer are really interested in how your trip was, because it's your third big trip this year ... and it's only April.
When you have to stop yourself mouthing the words to the Qantas safety demo in sync with the video because you know it off by heart and it's like one of those songs that get stuck in your head.
When you go to a travel show ... and leave within about 10 minutes because none of the specials are "specials" to you, and you have already been to quite a few of the overseas locations being advertised.
When you use your Frequent Flyer card more often than one of the credit cards in your wallet, or medicare card and it stays in there semi-permanently.
When your FF card has more magstrip damage on it from use than your credit card.
When you're on that many email lists for Airlines, Hotels and similar organisations that you receive more Flight offers than personal emails.