You'll only see this trick attempted by magicians who are very adept at sleight of hand. They'll ask for a coin from an audience member, bite it in half, and then hand it back to them. Sometimes they'll even magically put the coin back together.
The real trick here is quickly switching the real coin with a pre-bought prop coin - one that easily breaks in half when pressure is applied to it. That's why magicians are always very specific about the coin they ask for - it has to match the prop.