I have seen here that I should discharge myself electrically before touching the RPi? The presenter suggests a bare metal water pipe. I don't have this at hand. Are there other ways I can discharge myself? What does it mean to discharge myself?
All surfaces can build up a charge, in theory, either negative or positive. The science of electricity is the opposites of these charges will follow path of least resistance to the other charges, until they meet each other in equilibrium.
These static electric charges can build up strong enough to a point where they 'arc' like a spark across the air. The sensitive components in a micro integrated circuit will be rated for lower voltages to power and operate. When you arc a spark across these components, like when you get static shock touching a door, this spark can generate Thousands of volts (but low current), but enough power though to arc a spark across an integrated circuit and fry part of its core circuitry.
When these charges joint together they produce energy: light, thermal, electric current... A lightning bolt in the sky is produced by the same effect of these different charges coming together instantaneously, moving tons of energy.
To discharge yourself, you can touch a good electrical conductor like a metal of sufficient size to offset the charge built up in your body. Preferably something connected to a ground is ideal, like a desktop computer case should be grounded. You can discharge by rubbing your hands on that, like the bare metal, in the back of the casing. Plugged in should ensure it's grounded. A good computer service technician will have a static discharging wristband, a metal piece makes contact with his skin, channeling the charge out the wristbands conductive wire, that is tied to a static free mat that dissipates these charges and is wired to the Ground wall socket via grounding adapter that eventually finds its way to the ground (Earth).
The Earth is like a giant electromagnet, and all negative charge wants to travel through a conductive medium (path of least resistance) to join the positive in the Earth. These charges can become 'disconnected' and 'puddle' up on surfaces, like door knobs, people, static filled balloons stuck to walls... etc.
Water pipes are recommended because they are usually connected to the same metal structure as Protective Earth in your electric socket, so touching them sets you to the same potential as grounded electronic appliances. However, most USB power supplies are isolated, not grounded, so the effect is not as direct for a USB-powered RPi, but it still helps. Isolated electronics tend to settle close to protective earth potential due to leaks in power supplies.
Touching isolated metal objects won't help, unless they are very large.
In the absence of accessible ground potential, two things help a lot:
Moisture. Static electricity only tends to build up when the air is dry. A few shots from a water sprayer in the room where you will work (especially around the place you will sit) eliminate the problem almost entirely. Don't spray water on electronics though!
Touching ground first. Make a habit of touching the grounded parts of your RPi (e.g. USB connectors) before touching anything else. This way, the ESD will dissipate without having any semiconductor parts in its way, and will do no harm.