Cameron Diaz and Justin Timberlake
06/23/2011 at 10:30 AM EDT
Once a couple
in real life, Justin Timberlake
and Cameron Diaz
are now costars in Bad Teacher
– which contains what the comedy's director Jake Kasdan tells PEOPLE is the "most uncomfortable sex scene in history."
Diaz doesn't disagree, telling PEOPLE about making love to Timberlake (both with their clothes on): "Yes, yes. It was just [an] absurdity, a form of hilarity for all of us involved. We went to work that day and said, 'What time do we start being ridiculous? ... Eight o'clock? Perfect.' "
When it came to persuading Timberlake, 30, and Diaz, 38, to reunite for the movie (it opens Friday), Kasdan said that arm-twisting was necessary "only in the most minimal way. I'd say, 'Cam, what do you think of this?' And she said, 'It's a great idea.' And then we went and said, 'Justin, come do this,' and he said, 'Yeah, let’s go.' "
The two were together
from 2003 to 2007. She and Alex Rodriguez are now an item and have been for the past year
As for getting Diaz and TImberlake to make love in front of the camera, the director said, "I guess the real truth is that they're good friends … They're buddies."
To say nothing of professionals. "They got in there and started doing it," says Kasdan. "And it was so funny, we just couldn't stop shooting it. And we were doing it almost the whole day. And really crying, laughing at the [video] monitors."