Fun. Everyone's got a version of this sauce: sydnius has a Vietnamese version at nuoc cham, and I have one too. However you make it, at its best it's an intoxicating melange of sweet, salty, spicy, and sour flavours, much prized in Thai cooking, which is how I learned it. Here's what you'll need to make it like anthropod does:
Heat the vinegar, sugar, and salt in a small pot for a few minutes, stirring occasionally until the sugar dissolves. Then reduce the heat and simmer (don't boil) for about 10 minutes, stirring occasionally, till slightly thickened. Add chili garlic sauce and let cool.
Some people add strips of carrot or coarsely chopped peanuts to this sauce before they serve it.
In Thailand, as the venerable sneff says, this sauce often accompanies grilled chicken. In restaurants here in Toronto, it's almost always served with fried spring rolls or fresh salad rolls.
This simple sauce will keep well in the fridge for a week or so. It may not last that long, though: it's addictive, and you may find yourself spooning it over everything in sight.