I was an I&I corpsman for a while, we got a new I&I 1st Sgt. He came straight from PI, I&I was his sunsent tour before retirement. I was afraid he would be, well, a DI. Turns out he was one of the coolest guys I had ever met and he would have the rest of us rolling with his stories. I recall, though, asking how much of the DI persona was for-real vs an act, and he said the hystrionics were 100% acting, but acting for a purpose.