NO!

Well that is his favorite word right now. It doesnt matter what you say to him, if you say something and it sounds like a question he comes back with a loud and stern "NO". "Jeb do you want a drink?"-NO!, "It's time for a diaper change"-NO!, "DO you want a million dollars?" NO!
I thought I would be clever and stop saying No to him. If he did something wrong I would say "stop" or "don't".

Well -I will need to be more clever.

Yesterday at Gramma's house he told her "DON"T!" three times.