...you show up for a Cat 5 race on a protour-caliber bike. It looks a little silly if you actually win, and it looks amazingly silly if you don't make it to the podium. Wait until upgrading before buying any piece of equipment with a decal that says "Zipp," "Record," or "Bora Ultra."
...you are on a team that comprises almost half the field in a road race and yet can't put a single rider on the podium. If you are on a team, learn and apply some team tactics; otherwise, you are merely a bunch of people in matching jerseys.
...you sit mid-pack and complain about the slow pace, about having to feather your brakes on the descents, etc. Please understand that a bike race isn't about riding fast -- it's about crossing the finish line first.
If I think of any more silly things I saw this past weekend, I'll let you know.