I was in a short underpass tunnel today when a C63 sedan behind me downshifted/rev-matched. I hadn't noticed him before he did it, and it scared the crap out of me! I've seen them around town and heard them take off from stoplights, but had never heard one downshift in an enclosed space like that. Wow was it loud!
He had his window down and we chatted at the next light. Nice guy--said that his exhaust was completely stock! Always nice to talk to fellow car guys.