Originally posted by Superboy Prime
He didn't say their attacks wouldn't hurt him; he said he would just survive them. There is a big difference there.
big difference being that if he said "i won't be hurt by any of your attacks, the same does not apply to your friend" he wouldn't be putting the fear of god into them. this is basically a "i'll kill him because i can and you can't stop me, so shut up and listen."