From a high-pressure belly, your fart might propel you upward and forward. Come to think of it, that's exactly how your car is powered: A 700 bar, 600 liter, 3 second, noisy fart 😆 [Hopefully without the methane and the smelly compounds]

Okay, so it's just compressed air. Easier. But crappy specific impulse (less than 50 seconds). Even assuming that 50% of the mass of the car is the compressed air, that gives you less than 10s of useful thrust (with thrust-to-weight ratio larger than 1.0). Probably more like 5 seconds, actually. So the car must be an empty, lightweight shell containing big compressed air tanks. Cute demo, but totally impractical. But of course, you knew that.