Ben Affleck Jokes About Having a Very Unhappy Resting Face

Ben Affleck is clearing the air on what he says is a widely held misconception -- that he's totally miserable most of the time ... even when he's pretty damn happy.

Ben was on "Jimmy Kimmel Live" Tuesday to promote his new movie "Air," and the guys chatted about a number of things, including Ben's RBF ... y'know the thing he went viral for at this year's Grammys. You'll recall, he looked very unamused as his wife Jennifer Lopez danced alongside him.

Now, Ben cleaned it up a bit for Kimmel, instead of "resting bitch face" ... he said, "I have a very unhappy-looking resting face."

The guys joked Ben's face played a key role during a Christmas party Ben and Jen threw. They'd invited Jimmy and his wife, but as JK put it, "It did seem like you weren't quite as psyched about the party as everybody else".

Ben then tried to address the issue once and for all ... by showing a range of emotions on his face.

Amused and content looks a lot more like pissed off and I'd rather die than be here.

Hey, he's admitting it, but BA says don't blame him ... "That's how God made me, you don't have to punish me for it!"

Of course, Ben and JLo recently attended the "Air" premiere ... and the two looked happy as ever together, as they locked lips and took photos.