A corner reflector is literally just a couple of mirrors at a right angle.

It's 3 mirrored surfaces at right angles, yes. However the purpose is to reflect the light back where it came from, and if you want to do that accurately over a significant distance the right angles have to be very precise.

Say the laser-toting miscreant is 100m away and you want to direct the beam back onto the hand holding the laser. For that you'll need the right angles to be correct to within around 0.05°. You're not going to do that by gluing mirrors together by hand. (That isn't to say that you couldn't make a useful one by hand, depending what you're trying to achieve. Just illustrating the precision calculation.)

The expensive prism reflectors gp linked are even more precise than that. They say 3 arcseconds, which is less than 0.001°.

There are corner reflectors placed on the moon for precisely measuring the distance to it. I bet those are really precise ones.