Why hydrogen is called naughty element?

Hydrogen is known as a naughty element as it has only one electron in its valence shell so either it can accept an electron or donate that electron. It can do both of these things, unlike other elements in the periodic table.

It can either be placed with metals of group 1 or with halogens of group 17.

So, it is known as a naughty element due to its jumping nature from metal to non-metal.