Fiona, there've been times when my hair bugged me so much that I too wanted to get out the clippers and buzz it all off. The closest I've come to doing the full Britney, though, was a couple years ago when I gave myself a #4 (somewhere between 2 and 3 cm long). I hadn't warned anyone in my family what I was going to do, and when my younger son saw me, he busted a gut laughing. It was in the middle of winter like now, so I had to unearth my collection of beanies to keep my ears warm. It felt great, though, next to no maintenance and very little shampoo required.
I've never cut it quite that short since then, but it definitely has its good points. It's not hard to see why so many guys go for the shorn look. With women, though, the assumption is that either 1. you're having chemotherapy, 2. you're raising money for cancer research, 3. you are a lesbian separatist, or 4. you have recently been ordained as a Tibetan Buddhist nun.
