I divide the people I don’t greet into four groups.

There are those whom I don’t greet in order not to compromise myself
This is the simplest group.

Next, there are those whom I don’t greet in order not to compromise them.
This requires a certain amount of attention.

But then there are those whom I don’t greet in order not to get into their bad books.
They are even harder to deal with.

And, finally, there are those whom I don’t greet in order not to get into my bad books.
This takes a particular amount of concentration.

But I’ve had quite a bit of practice, and by my manner of not greeting people I manage to express each of those nuances in such a way that no injustice is done to anyone.