Easy, I said. Whose head would you like to be on it? He chose his own, which showed me that he had no idea what a cryptocurrency was. They are not physical coins, so don't have anyone's heads on them.

Never mind. Most people don't understand these things. This is good.

Things you can sell to unsuspecting friends as Bitcoins: 1) game arcade tokens; 2) foreign coins; 3) toy medals; and 4) chocolate money.

But one of my more serious colleagues is starting his own cryptocurrency; so I know the system.

Download the main coin mining software from a website called Github, then hire a nerd, as you have to tweak the programme (with C++) to make it unique.
Think of a theme. It is impossible to be too wacky. For example, one person made a cryptocoin called "Offerings to Cthulhu", named after an alien from a 1928 sci-fi story. You'd think that was too silly to work, but it is going strong after several years.
When people start buying your currency, sell them all and run away as fast as you can.
If the last part of this process reminds you of anything, it should.

It is the same technique used by people working for criminal gangs ("banks") for pushing evil scams such as sales of stocks and shares, unit trusts, investment bonds, Ponzi schemes, etc.

It's an exciting field. In January this year, the value of Bitcoins was going up and down so fast (in a $10,000 range) that you had to discuss it with a live price tracker in your hand. Here's a typical conversation: