Never watched the show, need help finding a scene

A commercial I saw numerous times had a line I found pretty amusing. Something reminded me of it today and I made a joke that fell on deaf ears, so I went to look it up, and had no luck.

I am 90% sure the scene is jonah and garrett in a (slightly?)darkened room, and sandra walks in and says she got a new something(shirt?). She then elaborates, "it came in a bag". To which jonah amusingly replies, "a bag, wow!"

Even if no one can point me to the episode this came from, I would also like to know if the jonah character is always that sarcastic, and in general if the humor is as....different. I may just start watching and find it the hard way:).