[header] How to argue with someone who thinks they are always right [title] Figure out the underlying cause. [step] Know-it-alls generally fall in one of two categories (or a combination of the two). Some know-it-alls have a deep sense of insecurity, and they try to cover it up by knowing as much as they can. 
Others actually do think they know it all, so they feel compelled to offer their knowledge to others. Knowing where the person's argumentativeness stems from can help you better deal with situation.