"The Ol' Jim Halpert" is the phrase used to describe your facial expression when you are caught in an awkward, uncomfortable or undesireable situation. The term is based on the facial expressions of the character Jim Halpert of the hit television show, The Office.
Person 1: Lets loose a long and luxurious barritone bung-fart while imitating his obese boss. Person 1 then gets out of his chair and starts to walk the Sumo-Wrester while throwing cookies at his face Cookie-Monster style.
Person 2: Sits in grave silence as Person #1's boss quietly has witnessed the entire display from the table across the room. Person #2 has no options in this awkward situation and simply gives his dinner date "The Ol' Jim Halpert" look.
"I'm not familiar with that" is simply a term to use when you're caught red-handed.
Cops: We caught you driving 75 in a 25.
You: I'm not familair with that.
Girlfriend: It's over! I saw you kissing Beth, you jerk.
You: I'm not familiar with that.