Adding Wheels To A Moving Car

Expecting the design or development team to scope a feature without definition or complete explanation while the product is being built.

Them: "How long would it take you to add this feature to the product?"
You: "I'm not sure I understand what the product and feature even is, let alone how to estimate it."
Them: "Well, just give me a ballpark..."
You: "That would be like adding wheels to a moving car."