When I was a kid grownups called me Peanut because I am short.
Related, DH and I call each other "G" which is short for "goober." When we first started dating we were disagreeing about something and I said "You are such a goober!" and he said "I am not! YOU are a goober!" And so it went, back and forth, and it stuck, and we always called each other "goober" after that. Over the years it got shortened to G. People that know us both call us "The Gs." The only time we use our real names when speaking to each other is if we are angry.