Learn how to wave.
Back in the days of rec.bicycles.racing, an internet bulletin board, there were several discussions that could never get resolved. There was tubulars vs. clinchers. There was Campy vs. Shimano (yes, it was that long ago). And then there was wave vs. no wave. But that one was pretty easy resolved; only an asshole doesn’t wave.
Learn how to wave.
Always wave unless you are so tired that you can’t lift your arms or it is unsafe to do so. In that case just say “Hi”. Bicycling is so much better when waving and greeting are practiced.