please, enlighten me

I have one question to the women out there. Why must you file your nails in public? Seriously.

Today, I was at a conference listening to a keynote address from an awesome speaker. Everything is going fine, then this woman comes in ten minutes late and sits two seats away from me. First, she opens something up to eat, which I'm totally fine with, but afterwards, she breaks out a file and starts filing her nails. She totally wasn't watching the speaker, but she let out a few laughs here and there. This wasn't a short nail fix-up either, she was filing for probably 30-40 minutes. It was like she doesn't cut her nails, she just files them down. Every finger got some attention. Not only did I find this slightly annoying, I find it a little unhygienic. I was probably breathing in her sloughed off dead cells and she didn't have a care in the world.

Seriously, I don't cut my hair while I'm taking the bus. Or trim my nose-hairs in class, but why is it that I see women filing their nails in public. What makes this socially acceptable? I don't get it.