I learned this lesson the hard way. Out on a ride with hubby when a van came up behind us and then squeezed between us and oncoming traffic while honking their horn. It almost caused a collision with an oncoming vehicle. As I was giving them the one-fingered wave, I see a young lady in the passenger seat of the van waving back. That's when I realized it was a family from our church who recognized us on the bikes and was trying to get our attention to say hello. I no longer give the one-finger wave. You never know who is behind the wheel or if they will vent their rage toward you at the next bicyclist they see.