I sense another Europe vs USA debate Personally, if the fries are fresh and tasty I think they're best simply with salt, but it's also awesome with good mayonnaise. I don't mind eating them with ketchup but if it's good fries it feels wrong to be tasting ketchup instead of the delicious fries. If it's cold or slightly old fries then sure - drown them in ketchup or even kethcup, mayonnaise and mustard! I haven't tried them with vinegar, it sounds weird but I'll give it a go sometime. Is it a particular type of vinegar that's typically used?