It sounds quite disgusting on the face of it, and if you google it you are met with a 50/50 mix of aerodynamic research links and, well, go look for yourself...
I was first introduced to this term back when I was finishing off my PhD in automotive engineering. I shared an office with mainly aerodynamicists, and they once told me about this strange work in the area of self-soiling cars.
It turns out that it has nothing to do with getting caught short inside your pride and joy, it actually relates to the kick-up of dirt around your car when driving. We have all been there haven't we? When you have just finished washing your car, the heavens open, and it starts to rain. Driving on any road with even the slightest amount of water on it will see the entire rear of the car being covered in a layer of road grime. Leave it uncleaned for anything over a day or so and you run the risk of transferring this dirt to your clothes when using the boot, or worse still, phallic artwork adorning your car.
It's actually the former of these two issues that concerns automotive manufacturers, forcing them to embark upon some high-level wind tunnel testing and computer simulations to try to force this dirt away from certain areas.
By sculpting the fenders and roof-line differently, aerodynamicists can force the dirty spray associated with wet roads away from key areas such as the door handle and window. This would mean that after a long slog down the motorway in the rain, you wouldn't have to worry about getting your hands dirty when using the boot.
Is this a genius idea to solve a real-world problem, or a waste of money for a non-existent problem? Let me know in the chat, and I'll pass it on to the research team!