It looks like like Boris has got himself a nice pair of skin-coloured board shorts. That's what we first thought, anyway - until we squinted and realised our new Slovenian friend was cheating and getting even more sun than the rest of us.
This was Tulum, Mexico, site of ancient ruins, the whitest sands, the most turquoise of seas and evidently, the most clothing-optional beaches in Central America. Just a quick drive down the road from the tourist havens of Playa Del Carmen and Cancun, this was the first major stop on the Central American odyssey for me and my group of 12. And thanks to Boris, we weren't wasting any time in getting to know each other.
In fairness to Boris, his wife Katyia was just as keen to throw off her tourist clothes after a morning's ruin-hopping, but there was something about her smiling bald-headed husband that made him the preferred target of our gentle nudist harassment.
This is one of the great things about doing an Intrepid tour: there is no age limit, unlike many travel companies, the result being the most random selection of travellers you could conjure up.
Here we had a 27-year-old Kiwi radio announcer, several English people in their 20s and 30s, ranging from chemical engineers to school teachers, an Irish girl of 28 who racks up big sales for Google (when she's not singing in her band The Corrs - she kept denying she was one of them but we knew), a 42-year-old Mary Lambie-lookalike dance teacher from Wales, a Dutch electrician of a similar age, a rich Iranian 22-year-old studying for her PhD in biofuels and, most spectacularly, a nudist Slovenian couple in their 40s who now work as journalists in Washington DC.
Add to that mix Sammy Hidalgo, our 28-year-old Guatemalan tour leader and that was our bunch for the next two weeks.
Sammy and I bonded straight away: "You're from New Zealand? You're not in Guatemala now, Dr Ropata."
It emerges that everyone in Central America has met a Kiwi somewhere along the line who has mentioned our beloved long-running soap.
Sammy told me all about the YouTube nights he and his friends have had watching Shortland Street and apparently there are even T-shirts with a picture of Temuera Morrisonsaying: "Dr Ropata's Medical Team." But Guatemala was still to come. Here we were in Mexico's Yucatan Peninsula, the hottest place I'd ever been. Just as well we were going to get some serious relief from the 40C heat in the form of some snorkelling .
Tulum is a vast stretch of white sand, famous for its Mayan ruins. And it has become a backpacker haunt with cheap beachside resorts. We'd seen the ruins, marvelled at how they were built in AD700, spotted enough iguanas to last a lifetime, watched turtles hatch and make their way to the sea, swum in the Caribbean waters (with or without trunks), and perspired so much that the sunscreen on our foreheads had blinded us.
It was all breathtaking but after several days it was time for something different. And here it was. I've snorkelled in New Zealand, Australia and Southeast Asia, but never before had I been clutching a torch and dodging stalactites and stalagmites. Sammy had taken us to the Cenote Dos Ojos caves where the water was cold enough for the locals to recommend wetsuits, although I wasn't having any of that nonsense.
Snaking my way between the rock sculptures, parting the schools of fish and marvelling at the strange glory of my underwater torchlight through the fresh water, I realised I was doing something I'd never ever done before. Moreover, it occurred to me how once you reach a certain age it is rare to do just that.
This was rammed home even more when we saw a couple partially submerged, still dressed in their wedding get-up. Posing for photos in this most photogenic of caves, they lounged about in suit and gown as if nothing was out of the ordinary. You're posing for wedding photos while underwater but still dressed? Add in the nearby dive-bombs we were doing off the platform into the cave and I could only hope they were having as much fun as we were.
Now this was something I'd certainly never seen before. But spare a thought for Boris, the Slovenian nudist. He'd never been so distraught at this unnatural marriage of clothing and water and said: "The only suit I wore on my wedding day was my birthday one."
Tim Roxborogh was assisted to Central America by Flight Centre. He hosts the Easy Mix Breakfast with Alison Leonard.