[ Dismissive ]

Sometimes people conclude a critical comment with stating “because they don’t know what they’re talking about”.  It’s a huge statement to apply a broad conclusion like that, on anyone. 

It’s not kind to conclude so definitively and be so dismissive of someone you’re talking to. 

They probably think they know exactly what they’re talking about.  So already you’re in a friction of disagreement.

Before leaping to a generalisation like “they don’t know what they’re talking about”, get a little more specific.  Pinpoint where in the conversation you came to that conclusion.  And then maybe consider helping to resolve the friction.