It's funny that I come across this thread now, after only thinking about this subject Yesterday on a ride.
I always acknowledge other cyclists. Generally a hi, nod or wave and usually get a response.
However, there are some riders who just ignore the gesture completely. There is one particular rider who I've passed a few times now who glances and ignores the wave.
This is what happened again Yesterday. My initial reaction was of annoyance - how rude!
Then I asked myself why am I waving at strangers on bikes anyway? Well, the answer is simple; They are out enjoying and appreciating what I also enjoy and appreciate and I'm sharing my joy for it with them. I not waving to get a wave back, but just offering a friendly gesture. Whether someone chooses to acknowledge it is irrelevant.
Whilst I'm on my soapbox, I was riding over the hills near me last weekend and as I rounded a corner to quite a deceptively steep and quite long climb, I noticed a number (say 5) cyclists on their way up. I like this as it gives me something to chase, a goal if you like. It was obvious they weren't going at any serious pace. As I closed, they all cleared the left hand bend at the top apart from one guy. He was heavily built, around 35 to 40 years old and obviously decided it was time to get back into shape. As I caught him, he was less than 50 yards to the top and he got off his bike to push. I commented as I passed him on how he was so close and 'he'd get this climb' next time.
He seemed quite touched by the encouragement. And that is the point I'm making. We all share this interest and a friendly word to this chap just getting into this amazing sport will encourage him to persist and I'm sure one day easily get over that climb. Now picture the 'grumpy' cyclist I passed Yesterday passing him in the other direction on said hill. Him not giving a friendly gesture to an overwieght guy trying his best to get back in shape may effect this guys resolve in the process - now that would be a tragedy!
Rant over - well you did ask the question!
Andrew.