How cool or cold does it have to be before you switch from shorts to long pants?

More like around 50 degrees for me. Sometimes even wear a jacket and shorts.

@girlsmoke1975: Funny you should ask this question because I was just thinking how people start wearing jeans and sweaters or warmer clothing after labour day when it's still in the 80s and 90s. It's crazy to be tied to some archaic tradition instead of practicality. I would suffer from heat exhaustion if I did that, so I wear shorts and tee-shirt until it's cold enough to go into warmer clothing. And what's with the silly rule about not wearing white after labour day? Where did that come from?

Carissimi, I agree completely. I dress to be comfortable. If it is warm enough in the winter I wear shorts and tee shirt.

@girlsmoke1975: Right. It's common sense to dress for the weather than some set date on the calendar.