I'm going to get really mad at my friends during our vacation
Why you get mad at your friends during your vacation?
They always wear these matching outfits and they're really annoying.
If they enjoy wearing matching outfits then that's what they want to wear. They're having fun, so just let them have their fun.
I hate looking at them and they make annoy me, I plan to say something to them.
If the habits of your friends annoy you so much, you should not go on vacation with them. It seems to make you unhappy so you should plan a separate vacation and be with people that will make you happy. Don't ruin their good time to spite them.