Well as long as weed stays illegal I wouldn't want to smoke it anywhere except in my house.
And since I'm living with my parents that option is gone.
I just wouldn't want to be high in public. It's not even about getting caught by the cops. Let's say you run into a new acquaintance, co worker, boss etc then it could leave a really bad impression.
It sound weird by I'm obsessed with keeping a good reputation. Same reason my facebook profile is "cleaner" than anyone else of my age group.