HOWTO: Legally Ride a Bicycle in Italy

Now there's no real reason to completely comply with the law in Italy, but if you would like to give it a try, hopefully the following will give you an idea what you should undertake. Bear in mind though that the list only contains only items exclusively relating to bicycles; as a cyclist you will have to obey all the other rules of the Italian Road Traffic Law (Codice della strada, or Cds) and their respective execution directives (Regolamento di attuazione, Rda).

• tires are mandatory, and so are independent front and rear brakes, a bell (which must be heard for a minimum of 30 meters), a white or yellow front light, a red rear light, and at least one red rear reflector (which must be below the rear light). If you fail to abide by these conditions, it will cost you between €23 to €92 each. (Art. 68 Cds, Art. 223 Rda) 
• speaking of reflectors: practically speaking, your bike needs at least seven of them (two on each pedal, at least one for each wheel, which must reflect to both sides, and the abovementioned rear reflectors). All of them have to be yellow, with exception of the rear light. It'll set you back the same sum as above if they're missing. (Art. 223 Rda)
• if conditions allow it, two people can ride next each other, but only in towns, and not in the countryside. (Art. 182 Cds §1)
• you must always have at least one hand on the handlebar, and the other must have all the necessary degrees of freedom. (Art. 182 Cds §2)
• you are not allowed to give a lift to another person on a regular bike (Art. 182 Cds §5)
• it is mandatory to use bike lanes wherever they exist (Art. 182 Cds §9)
• you have to wear a reflective safety vest in tunnels (Art. 182 Cds §9bis) If you don't do this (or don't respect any of the previous three points) it will cost you, you might have guessed it, between €23 and €92.
• bikes have to be pushed in heavy traffic, or in general where the conditions require it (Art. 377 Rda §2)
• you have to use your arms to signal your intention to turn; you have to raise an arm to signal your intention to stop (Art. 377 Rda §3)

Some examples of illegal behaviour:

Not enough degrees of freedom (her right hand, not Italy)

This road is not large enough for both of us.

You noticed that the reflector is placed above the rear light, haven't you?

In Italy they would all be walking.

Thanks to BikingInRome for the shoutout!