Nick Diaz has stated that he doesn't have a nickname. He is just Nick Diaz from Stockton, California.
Nick "El Diablo" Diaz
Nick Diaz's Nickname
If you look at Nick Diaz's fighter profile on various websites, he is referred to as El Diablo or Diablo. However, Diaz once said, "Who the f*** calls me Diablo" which evidently means he doesn't like the nickname that just got attached to him.
THE STOCKTON SLUGGER
Some Ideas for Nick Diaz's Nickname
Nick "Not Nate" Diaz
"Nick "The Elder" Diaz
Nick "Nunchuks" Diaz
Nick "Stockon Mothereffer" Diaz