That really sucks... can' say I'm surprised, though. Although I'm not a fan of broad generalizations, I do notice more and more folks these days react just like your Debbie Downer to any new ideas - they freak the eff out and start rattling off possible worst case scenarios. Heck, when I bought my bike and started riding a few months back, my dad even told me that I was probably neglecting my dogs now b/c of the time spent on my bike. Never mind that biking was a small part of a greater positive life change (going to rehab, quitting drinking, dropping a bunch of good old Wisconsin-style beer-induced belly fat), the only thing to focus on was the negative.

Honestly, you just have to tune that crap out. You're doing the right thing by encouraging your co-worker to be a bike commuter - there are just so many positives to it economically, health-wise, environmentally, etc. Don't let the fear-controlled Debbie Downers of the world get under your skin, it's just not worth it.