People giving opinions about things they have no knowledge about!

Do you often have such experiences?

Do you get annoyed when you start a discussion either online or in real life and some people start giving their opinions just to show that they know something. I am not talking about philosophical opinions, I am talking about hardcore facts.

 

Yesterday I was talking with friends about need of filtering water before drinking through reverse osmosis system and this guy came along saying that we should not drink filtered water because vitamin B12 gets filtered in the process and its very important for our body. I was very surprised and I just didn't understand how can somebody give opinion without any knowledge or prior research.