I want to tell my friend that my other friends weight loss was more impressive
Are you trying to make them feel bad?
Not at all, I just want to tell him that
It's good your proud of your friends who've been success at weight-loss, but rubbing it in to a friend who's been less successful isn't very constructive. You should have a talk with your friend and recommend a good dietician.
God I'm such a dick.
No you are not because you did not actually tell him that. You should make sure that you do not bring up the progress and success that one friend is having when you know that the other person is struggling.