My favorite is when someone installs the shoulder harness/belts through the stupid holes in the seats and they come out below your shoulders, during an accident, you will get spinal compression. Always have your belts positioned above the shoulders just slightly to minimize the angle and stretch in an accident.

1941 Taylorcraft
1968 Charger
1994 Wrangler
1998 Wrangler
2008 Kia Rio
2017 Jetta

I didn't do 4 years and 9 months of Graduate School to be called Mister!