I had many car giving me a "beep beep" as they pass me. Those folks are usually waving at me and some even has young child in the back seat waiving. My bike with the pannier, cargo box and whatever else setup make it obvious that I am a commuter. So most beep I get are just friendly gesture.

Then there are those car that are right behind me not willing to pass although there is plenty of room. Those folks are the one who likes to "beeeeeeep, beeeeeep". They are the annoying folks who believe they own the road.