So did your friend know it was dangerous and just ignore it, or was he totally clueless about the risk?

That popping sound really IS something you never forget. After mine went pop and killed my hard drive, I learned to look for safety features like OVP and UVP right on the box. Don't just grab a unit because it has a bronze badge, read the actual specs. A good PSU is the one thing you should NEVER cut corners on, trust me.