I don't really expect people to wave or call out hello all the time. More often than not I'll just smile and nod to someone I encounter on a bike, and if they say hi or wave I'll do so in return. If I pass then I'll call out, and say a cheery good morning and maybe a "howya doing" if it's an older person or someone who appears to be new.

What I consider rude behavior is more along the lines of zooming by very close with no warning, particularly on a narrow road with oncoming traffic, or zipping around me at a stopsign or a stoplight.