When someone speaks, acts or performs around others
in a way that assumes the other people already know the
basics. This can be fine for all parties involved, but it can also be considered rude, depending
on what the subject matter is and who's receiving it.
A friend invites you over for dinner with his family. During dinner, the relatives start talking endlessly about
Mortimer's problems. You keep thinking: "Who the fuck is Mortimer?" and no one at the table has the courtesy to explain to you who Mortimer is. The family was speaking "matter of factly" about some loser named Mortimer.
Snottrah: Do you want to come back over for dinner?
Perphenalia: Nah. Last time I was there everyone started talking matter-of-factly about some prick named Mortimer and I sat there like an idiot.
Snottrah: Oh, sorry. Mortimer's my meth addict uncle. We disowned him a couple of years back for holding himself at gunpoint and
carjacking his own car.
Why is the professor talking so matter-of-factly
about That's because you missed the first two classes, genius.