Suetonius's "Life of Nero" where his love of chariot racing is mentioned. It is important to note that Suetonius is a very biased writer who enjoyed telling every nasty piece of gossip he heard. It's not that the emperors were not abusive of their power, but their abuses were probably not as bizarre as Suetonius makes them out to be.
Collection of a variety of sources about Nero's trip to Greece.
This is probably one of the most well known examples of Nero's losing any sense of reality in the bizarre world of being a Roman Emperor.
Not everything Nero did was bad, here is a little discussion of his urban planning.