They may all be described quite elegantly with the same equation. Most real fluids have aspects of complexity once you look carefully enough. For example, it makes a big difference whether you use oil or water to lubricate your car engine. Such complex behavior may be explained when you look at the very smallest scales where things start to jiggle about because of Brownian motion. Or, if you look at a fluid interface, like that in a bottle of oil-water salad dressing you will usually find a whole forest of little molecules that like to be right at the interface and change its properties.
Detergent is made of such molecules, and they like to break the interface up into little bubbles.
Other well known examples of fluids with complex behavior include paints, toothpaste, clays, and mayonnaise. If you look at them just as a continuum and forget the small particles or molecules they are made of, the making of the model will be impossible.