have calluses from patting own back

have calluses from patting one's own back

 and break one's arm patting oneself on the back
Fig. to be a braggart. If you haven't heard about Bill's latest achievement, he'd be glad to tell you. He has calluses from patting his own back. Jane: I did a really wonderful job, if I do say so myself. Tom: If you're not careful, you'll break your arm patting yourself on the back.
See also: back, have, own, pat