What is a word or phrase that means a speaker (or writer) is talking about something they know very little about, but they think they know more than they do?

An example: If you read diet message boards, you get dozens of people saying ‘Eat 6 small meals a day,’ or ‘Eat 3 big meals, but don’t snack,’ or ‘Eat more/less protein/carbs/fat.’ Each person is sure they are knowlegable enough to give good advice, but real experts(dieticians or researchers, for example) are rare. I want a word to describe this attitude.

Bullshit is close, but someone bullshitting usually knows they aren’t an expert, they just want to convince the listener they are. Also, I’d prefer something politer than bullshit.