Are they Asian surfers?
We get people here who do that sort of thing, no matter what you're doing...
Playing street hockey in a huge carpark at the local park, at the far end away from everyone else? Some ass will ride his bike over and stop in the middle of your pitch.
Kiteboarding on the ONLY beach around the giant lake that's safe enough to launch and land? Someone's going to bring their kids down - not to the swimming beaches just down the road, but to your beach AND park themselves right in the middle of all your kites, not even bothering with the empty sand 100m to their left.
Landboarding at a different park? You guessed it, someone's going to come and play baseball right on top of you kite lines.
Humped your gear 500m away from the beach to get out of everyone's way? Yeah, here comes Fisherf**k to cast lines right where you're about to ride.
My fav though is still the guy with the powered-paraglider, setting up behind the kites and windsurfers, then trying to launch himself between the palm trees, over the gear, over the people on the beach and not tripping down the stairs. He nearly collided with all the above AND wrapped his wing in the power lines before he actually got off the ground. Naturally, the wide open spaces just 50m either side of that space was too far away

I can't decide if it's just congenital selfishness or absolute lack of consideration of the surroundings...