I also just sent them the following message:

I am writing to let you know that I do not find any humor in the t-shirts etc. for sale on this site that say "I don't share the road" and/or show a picture of a car hitting a bicycle. As a cyclist who rides on the roads (which is where bicycles belong--not on the sidewalks), I am disturbed that someone would have this type of attitude and sell merchandise that is intended to incite such violence. Free speech is one thing, but encouraging people to injure others and flaunting one's (supposed) willingness to do so is crossing the line. Thank you for your concern.