Dan,

It is one thing to “joke” and another thing is to undermine your ideas, etc. related to your work.  Those things should be separate.  Be direct about letting him know that you boundary is for him not to comment on your work.

His behavior is because he is insecure.  I am not sure if you can use that to your advantage by making him an ally and letting him know that you want to support him but regardless you need to set hard boundaries with him and let him know that such behavior is unacceptable when it comes to work.

Mark