Originally Posted by Turbo Joe

Just scratch/scribe the "cut line" with a SHARP x-acto knife, then fold the lexan back along the line and tear it. Sounds scary and tricky, but it's by far the easiest and cleanest way to do it. You just have to scratch it good and it tears perfectly smooth and straight.

Really tight areas you do with scissors or cut with a knife, but long straight or curved areas can be done super-cleanly in a few seconds.