If you're up for a real roleplaying challenge, try a game in which you play other members of your gaming group.
The game doesn't need to be set in the real world. Imagine yourselves as wizards and warriors, or pilots and mechanics, in a world of the imagination. But the characters are based on yourselves. Greg plays a thief with a personality based on Marcia. Marcia plays a cleric with a personality based on Bobby. Bobby plays a wizard with a personality based on Alice...
Hmmm. This could break up your gaming group faster than playing a cut-throat game of Diplomacy.
Greedo: Mia roleplaying, she'sa bellissima, no?
R2-D2: Are you going to talk like this all the time?
Greedo: I'ma staying inna character!
Greedo: Mia learna so much aboutta da roleplaying.
GM: I am so sorry. He's been like this ever since he ran his campaign.
Obi-Wan: Wait. Jim ran a campaign?
Greedo: Itta wassa gritty action-o-drama.
Obi-Wan: Oh my. How did that go?
C-3PO: It was great fun!
R2-D2: Yeah, it was... surprisingly entertaining.
GM: When you left suddenly, Ben, it threw my plans even more than usual. Jim stepped in and... yeah. We all enjoyed it.
Obi-Wan: I'm sorry I missed it.
Greedo: Sally filled-a in for you.
C-3PO: "You realise that would never happen in real life."
Obi-Wan: Okay, okay.
C-3PO: "Furthermore, I hate having fun."
R2-D2: We barely noticed your absence.