Spring
The reason is simple. How do you dress in the Spring? You wake up to beautiful sunshine so decide to wear a skirt and take a light jacket with you. At midday, it's snowing and when it's time to go home, you have to swim through the pouring rain. Grr...

There are good things about Spring though. Well, when I say things I mean thing. I love daffodils! They're the most improbable flower ever and I won't forget the first time that I saw one poking out of the ground of my high school. I'd seen the pictures, but couldn't quite believe they were true until I saw them in real life. Nice.
And daylight. After growing up in a country where the sun sets at the same time all year around (ok, there is about a half hour deviation) it's nice to have the sun set later and later during the spring. Gives you more time in the day and a spring (sic) in your step.