I'm sure many of you have heard this story before... in 2007, a 60 year-old Japanese housewife made headlines for receiving a suspended sentence and fine of 34 million Yen for tax evasion having made 400 million Yen (USD3.44 million) trading forex! (Source)
The obvious lesson notwithstanding (i.e. do not mess with the tax authorities), it's a useful simple benchmark to use. So, are you a better trader than a Japanese housewife? ;-)