Hey! What you're doing there is REALLY unsafe. You're going to get yourself killed! And everyone around you, too! Are you some kind of idiot?Here's another ineffective way:
What are you doing? [walks away]Here's how I might approach someone doing something unsafe:
Hey, uh, have you thought about the safety concerns with this method of doing something? No? Let's go look up some best practices on how to do this.
I know that you're under pressure and trying to get this done -- I really appreciate that. But let's go find out if you could get hurt, eh?That might be a little too diplomatic. It depends on the person you're talking, of course, and what approach you think might work the best. Readers, what do you prefer?