Do you know if they even saw you? If they were chatting they may not have noticed you.Out on a ride earlier, I spotted about 8 riders from a club on the side of the road, talking. As I went past I waved at them but they ignored me so I shouted: " Ignoring me then". One of them must have heard me because he turned round and waved. All the solo cyclists I see always waved back so I conclude it must be a club thing. Being in a group of usually faster riders, they must look upon solo riders as inferior. Like I said, a bunch of snobs not worth the trouble.
Why do you care?