Hi straight. I’m narrow.

The trick is to never look away. Stare till they notice, then keep staring. Have to get up to use the restroom? Maintain eye contact as long as possible and reestablish it the moment you’re back in sight. If they get up, the responsibility to maintain that eye contact is on you. Make sure to stay within eyesight, following them if necessary. This is your chance, we’re rooting for you!

Why do you feel you need to convince them of anything? I totally get having your eyes opened to the broader spectrum of coffees available but end of the day it’s a preference based on subjective senses. Let 'em do them, what’s the harm?