Sacha Baron Cohen Jokes with O.J. Simpson About Killing Women

Sacha Baron Cohen saved the best for last ... wrapping up his 'Who is America' series by sitting down with O.J. Simpson, and trying to get him to admit he committed the murders.

O.J. didn't take quite the bait, but it was pretty close as Sacha went undercover as fictional Italian playboy Gio Monaldo and joked about killing his gf, who pretended she had no idea who Simpson was ... that is until Sacha makes knife-to-throat gestures.

Simpson's reactions are uncomfortable, awkward ... but totally priceless. He appears to be completely duped. Gio and Simpson even laughingly suggested a bungee cord plot to kill Gio's gf.

Even when Simpson tried to get Sacha to stop, the comedian kept pressing. Watch ... we're glad he did.