To be with a pessimist is to know that you are with a pessimist. But you can be with a nihilist and have no idea. Indeed you could yourself be a nihilist and have no idea. Such a lack of awareness is the point of nihilism, as nihilism is all about hiding from despair rather than dwelling on it.

Is it OK to be nihilistic?

You are right to reject it: nihilism is harmful and mistaken. However, it is not an abstruse philosophical irrelevance, because everyone falls into nihilism at least occasionally. I'll suggest that you may be more nihilistic than you realize, and it may be causing you more trouble than you think.

What makes someone nihilistic?

This often includes assumptions about society: its institutions, values, customs and beliefs. ... Philosophy has been accused of causing nihilism, by undermining existing values and beliefs and failing to put anything useable in their place.