Fixies are a raging fad now, but are $1200. A unicycle is a fixie that costs $100.
I love flatland BMX (video), but most of the time, they're imitating a unicycle. So, why not start with that?
How many women skateboard or BMX?      
They are noticably smaller. You can carry one for long distances, so you don't have to lock them to bike racks, and you can keep it in your cube if you commute. You can fit at most 2 bikes inside a sedan without layering, but you can get 5 unicycles in one. You can also travel on a plane with them in a duffel bag.
If you think there are some things bicycles can do that unicycles can't... you'd be wrong, wrong, wrong.