Learn English – the word that describes a word that can mean anything

“Idiosyncrasy” is a great word for referring to the unique things a person does, while “mannerism” might suit certain uses better as a more general term:

mannerism

noun

1. a habitual gesture or way of speaking or behaving; an idiosyncrasy.

_{Source: Definition of “mannerism” in Oxford Dictionaries}

For instance, I might say “[my pet] Aki has an idiosyncrasy where he's prone to running in circles when it's snowing at night.”¹ That is a specific behavior that is unique to that particular individual.

Conversely, I could say “David Cameron has adopted all the mannerisms of Tony Blair, including using his hands a lot to show he's sincere.”² Many people gesticulate or use their hands while talking, and some patterns resemble one another, so this is not an idiosyncracy of Cameron or Blair, but a common mannerism that they purportedly share.

"Norm" is neutral by default. Any negative or positive connotation is implied by context.

When you visit another country, you should always try to follow societal norms so as not to cause offense.

How can I follow those so-called "norms" when I don't want to be anything like the other kids at school?

In my first example sentence, "norms" is neutral or slightly positive to mean "what is common and courteous". In my second example sentence "norms" means more like the negative "what everyone else does because they aren't original or interesting".

Of course, a "norm" is a matter of perspective. What seems normal to one person might seem outrageous or even offensive to another. Again, context is everything.