>>12310321Diet coke has less sugar and more carbon dioxide than regular coke, which moves the ph down a little bit and makes it more corrosive, which means that it picks up more BPA from the lining of cans and bottles than coke.
Regular coke has shitloads of BPA issues already so a diet coke lifestyle will probably have smaller and less functional testes than a coke lifestyle. All of this comes from the lining of containers, though.
If you drink entirely out of sterile glass containers the only issue with diet coke is tooth decay, which isn't very much.