Really wish people would stop trying to pathologise Nick and his behaviour. Most people that do bad things are just bad people, giving people diagnosis just makes it seem like they're not entirely in control of the their actions when in reality they likely are.
Nick does not have ODD, NPD, OCD, BPD or ADHD, he's not a psychopath, sociopath or depressed, he's just a selfish, arrogant, nasty little man who's had all his worst traits amplified by a mixture of chemical abuse, bad decisions & an overabundance of praise for doing practically nothing of note his entire life - were the banality of evil made into a sculpture, it would look like Nick.