...if you've almost concussed yourself on the window in a car from making an unexpected sharp left turn. (or right, if passenger.)
...if you've inadvertently punched the window instead of reaching for the turn signal lever when you do end up driving.
...if one of the guys on the local track bike team does a double take and then starts a discussion about your commuter rig. (I'm still proud of that one...and I really miss that bike!)