The method I found best to ease a fellow Americans worries about learning SI units is to start small and work up to bigger units. For example, when talking about length, start with millimeters. Get a measuring tape and go up to about 10 mm. Now, show them that equivalent in centimeters. 10 mm= 1 cm. Next, work your way up in cm. Go to about 100 cm. now explain its equivalent in meters. 100 cm= 1 meter. Its a basic way of teaching but I personally found it pretty effective.