Some people are jerks. There will always be a few. He was probably bored and looking for something to amuse himself, I've had people do similar things while abroad or sometimes just sitting in the pub at home. It's not worth even thinking about... I mean there's billions of people out there and that's billions of (sometimes idiot) opinions you don't have time to worry about. Especially on holiday.
Least you could leave the guy behind at the end of the excursion, right? In Austria one time I was stuck sharing a table at a hotel for a week with a dude who wouldn't shut up commenting about the age difference between me and my partner. Every mealtime. Wasn't about to let him ruin an £800 trip.
There's only one outcome if you let it get to you. You lose out and feel lousy. Just imagine them sitting on the john or something. Don't take people seriously who don't deserve it...