First, julienne your carrots by peeling them, cutting them into 2 to 3 inch pieces. Then cut those pieces into rectangular planks, then cut those planks into a matchstick shape. You can also use the julienne setting on a mandoline, just be sure to use cut resistant gloves.
In a medium saucepot, bring the white vinegar, rice vinegar, water, sugar, and salt to a boil. This is your brine.
While the brine is heating, place your carrots in a 1 pint mason jar.
When the brine has come to a boil, very carefully pour the brine over the carrots, leaving about an inch of space at the top of the jar.
Let the jar cool to room temperature, and then place the lid on and stick it in the fridge.
Quick pickled carrots can be eaten immediately, but the flavor improves with a few hours in the fridge.
Use within 2 weeks.