Justin Bieber Having a Ball After Dinner

Justin Bieber is either nuts about pressed juice or just one happy-go-lucky kinda baller after dinner.

We got the Biebs grinning ear-to-ear leaving Il Pastaio Tuesday night in Bev Hills ... and we gotta ask, what triggered such a huge laugh?

Here's what we do know -- his swollen balls triggered a lawsuit back in May after "an immoral employee" sued the hospital where Justin checked into for what turned out to be a swollen testicle.

Someone cue Jerry Lee Lewis' "Great Balls of Fire."