Which, as the responder may know, is usually my response when others extend similar invitations to me.
A lot of truth is packed into that response. There's the hint that even if the inviter does go first, the responder won't go second. There's the acknowledgement that accepting the invitation is a good idea, and the confession that it's a very difficult thing to do. There's the challenge to the inviter: is he all talk? There's the accusation against the inviter: he hasn't accepted his own invitation yet.
Ridicule directed at a nutritionist who doesn't follow his own recommendations may not harm anyone else, but if ridicule is directed at his recommendations, then -- assuming they were sound -- he has harmed those he set out to help. Better to be silent than to scandalize people against a healthy diet. Much more so with spiritual and moral truths.