I don't see a real problem here. "who thinks he's my manager and talks in a way like he knows everything" If other person's thinking and talking irritates you

I don't see a real problem here. "who thinks he's my manager and talks in a way like he knows everything" If other person's thinking and talking irritates you - the best way is not to respond. Ignore and he moves on. If you eager to convince him that his way of thinking is not the right one - i think you got a bigger problem.