mild meltdown

I made a quick trip to Washington DC 2 days ago for a school project. I dutifully put my 'liquids' in a quart sized plastic bag. When going through the security, the lady at the scanner said that my face wash was over the 3.4 ounce limit (it was 5 ounces). At the time, I was really upset that I couldn't just dump out 1.6 ounces of it and keep the rest. It was brand new and really good face wash! It didn't help that I had woke up with a migraine headache that morning. I argued with several security personnel and I'm surprised they didn't threaten to arrest me. All over $7 face wash.

Part of me is still mad because it seems so arbitrary. Why is 3.4 ounces of face wash OK and 5 ounces is unsafe? On the other hand, it was only $7 and probably not worth the frustration. I just need to learn to chill out.