It was my own fault, I know. The rule stating that liquids, gels and aerosols in carry-on baggage must be in containers of less than 100ml and passed separately, in a transparent zip-lock bags, through the X-ray inspection is hardly hold-the-front-page news. I forgot about it - but the half-empty 50ml squeeze bottle of hand sanitiser in my shoulder bag was picked up by an eagle-eyed guard.
Fair enough, but here's the thing: I was on the fifth leg of an eight-leg round-the-world journey. No one had noticed in Los Angeles or Frankfurt - two of the world's busiest and, presumably, most eagle-eyed airports - or in Madrid, a city actually attacked by an al-Qaeda cell in 2004.
But as I went to board a 40-minute flight out of charming, retro Lisbon, they hit the roof. I was dispatched, with a good telling-off, to buy, for one euro in a slot machine, a zip-lock bag. I binned the sanitiser.
I'm not complaining. Rules are rules and carelessness is carelessness. But I can't help wishing that there would be some standardisation of enforcement.
Once, as I left Auckland en route to Europe via Hong Kong, one of the security blokes noticed a tiny pair of scissors in a first-aid kit in my carry-on.
"Let's check out the blade length," he said cheerily, before ruling them non-lethal and waving me on my way.
"I must measure blade length," said an unsmiling guard in Hong Kong about 14 hours later. He grimly shook his head and tossed the (rather expensive, surgical-steel) scissors in a bin.
These shifting standards are frustrating for passengers - though it's a mild frustration in the overall context of air travel and, of course, can easily be avoided by not packing anything sharper than a thriller in your carry-on.
The bottom line is that I'm less hosed off with the Portuguese than with the folks at LAX and Frankfurt. What the hell were they thinking, letting a psychopath like me have free run of a long-haul flight armed with 30ml of Ansell Purell? If it were not for that second glass of whisky, which sent me into a deep sleep until the breakfast trolley came around, hundreds of innocent people might have died.
And while they're answering that, perhaps they might also explain how a poorly paid security guard can, at a glance, tell hand sanitiser from high explosive, just because it's in a one-euro ziplock bag.
So much airport security, it seems to me, is a kind of sympathetic magic, like voodoo. No one is looking for terrorist bombs; they're acting out the process of looking for terrorist bombs as a way of reassuring (whom? themselves? us? who do they think they're kidding?) that everything's under control.
The humorist P J O'Rourke famously described US foreign policy like this: "Wherever there's injustice, oppression, and suffering, America will show up six months late and bomb the country next to where it's happening."
Airport security is like that. The day after Richard Reid tried to blow up a plane in 2001 with a bomb in his shoe, a shoe bomb became the world's most improbable terrorist weapon. Terrorists try stuff that no one's tried before because it's less likely to be expected and thus detected. Meanwhile, at airports all over the world, little old ladies are removing their Kumfs for inspection. Go figure.