Originally Posted by DannoXYZ

There's two ways to pinch a tube. One is with the lever. If you get the tube caught between the lever and rim, then pry upwards to push the tyre over, you'll cut the tube. Yeah, I've seen it happen just as easily with the metal as well as plastic levers.

The other much more common way is to have the tube pinched between the tyre-bead and rim after installing the tyre. This is just as easy to do with metal as well as plastic. And the only way around this is to squeeze the tyre sideways and inspect the gap between tyre and rim all the way around the tyre on both sides. Many people people don't do this and end up with blow-outs soon after and think they had a defective tyre or tube.