First Step

When a lack of Common Sense is observed, call it out!  Politely, but call it out.  Don't laugh and walk away.  Ok, laugh (inside), then help the poor soul see the error in their ways.

When you see someone start to fill their car, smoking a cigarette, say "hey buddy, are you trying to kill us all?  Please put that out."  Don't laugh as he's blown into the next county!

Tell the poor guy that pours paint thinner in a glass and then sits it next to his glass of water that that might not be the best idea!  Don't laugh as you're dialing 911 minutes later.

Tell your friend that she must quit texting and driving - especially when you're in the car, too!  It's hard to laugh with a broken jaw from the airbag being deployed.

You get the picture.  Let people know when they're making obviously dumb choices.