['I am jealous of my coworker, he is very athletic and smart', "Don't worry about him.  Keep working on you.  I'm sure you have a lot of great qualities.", 'Thank you, I like to think that sometimes, but it can be tough']
I understand.  Its hard to not compare yourself with others but we're all made differently with our own strengths.  Try to shine with those!
I am jealous of my coworker, he is very athletic and smart