A San Francisco man paid $6,000 for a billboard advertising an AI chatbot with no AI behind it. Just him, typing every answer by hand. 30,000 prompts flooded in anyway, peaking at 5,000 per hour, and the project accidentally proved something dark about how people use chatbots. Tucker Bryant is a 32-year-old Stanford grad and ex-Googler. The idea hit him the day he caught himself asking an LLM whether to wear short or long sleeves on a 65-degree day in San Francisco. He'd lived there for 7…