Which Brother?

He gave me a look of disbelief. "I only have one brother."
Which was all well and good, but I had no idea who this person was or which brother he was referring to. "Cool, what's his name?" I asked, raising an eyebrow as he scoffed again. This guy obviously was full of himself if he continued to think I could read his mind and automatically know everyone's relation to each other.
He rolled his eyes. "It's Jeff." 
"Oh!" I smiled. Now I knew who he was referring to. "Mary and Phil's friend." 
He blinked. "Who?" 
Ah. Now it was my turn to raise an eyebrow. And he got annoyed at me because I didn't know who his brother was at first mention? How could he not know Jeff's friends? The ones he crashed on their couch for four months. "You know. Mary was my roommate and she worked with Jeff at the Hardware store."
"Oh." 
I could tell he didn't know who Mary was at all.
I silently sighed. 

-Inspiration from a work conversation