When refuse a project from a client?

Anything of the following:
- "I have a startup idea, it's a social network for <extremely specific/useless market>..."
-"It's like <famous site> but different..."
-"I have pretty high 2k budget, can you make me a website like YouTube?"
-"It's really simple, I need JUST a chat app like WhatsApp"
-"Can you create me a functional demo first?"
-"Can I be online in two days starting from now?"
...