I can't believe I forgot about this one:

A guy going the wrong way up Boylston St (busy city street). That would be bad enough, but it was raining, and he had an umbrella. The wind was right in his face so he held the umbrella in front of him, totally obscuring his view!

I watched with morbid fascination. Thankfully this guy eventually realized how stupid this was and put the umbrella away after maybe 20 seconds.

Edit: It also occurs to me that riding in a head wind is bad enough... I can't imagine the resistance he was getting with that umbrella open.