So this happened a while ago, but I told myself I would finish reading the thread first.
I had just installed my Invidia N1 and went to pick up my friend.
Friend: I thought you said you installed a new exhaust on this?
Me: I did (?)
Friend: Its really quiet
I totally forgot that he was 60% deaf in one ear and 40% deaf in the other.
He actually got surgery a few weeks later and when he got in my car again his ears were really sensitive and he held them during the ride. Kind of felt bad, but at the same time it was funny.