don't worry, be happy...
I know it's hard, but just ignore them. Your vacation is about you, so do your best to block it out. Avoid walking on the streets where there are a lot of them if possible. It won't do any good to tell off a few of them, they'll probably just think it's funny or not understand you. And I know some people may tell you just to smile, laugh and say no thanks, but being nice gets old really fast when you are forced to do it so many times.
It's not just annoying in Cabarete, even in Barahona I say there are more of and more annoying conchos than mosquitos or every male between the ages of 18-40 that owns a Suzuki 125 is a concho. If that makes you laugh, just think about it when they are bothering you to keep from blowing up! This may be even harder, but try to be patient and understanding. Realize that these guys probably didn't finish 8th grade in Dominican public schools in a campo (translate that to your country and you're looking at a lot lower grade level). The t-shirt suggestion is funny, but sadly enough some may not be able to read what it says. This is what they do and they are trying to make a living the best way they know how, and do it because it's worked before.
It sucks for people to assume that a white person/foreigner walking down the sidewalk is 10 times more likely to want a concho (and I thought the stereotype was Dominicans were the ones who don't like to walk far). It probably isn't that, just that when they do pick up foreigners, they can charge way too much and people actually pay them, so now you are the one suffering for it.
If you are seriously angry and annoyed, and will be there for a while and want to do something, write a letter or go talk to the sindicato of the conchos (if there is one) or the sindico (mayor) to complain about them and suggest ways they can be more professional. If you read/write Spanish, go to this website and post a complaint about conchos in Cabarete under the transportation forum:
QU?JESE.com.do | El portal de quejas y servicio al cliente de la Rep?blica Dominicana
A final practical tip I have is wear some dark sunglasses, which I call my "tiguere blockers" cuz then people don't even know you glanced in their direction and it's easier to ignore them. :cheeky: