A childhood belief about swearing

There's a Peanuts movie called Bon Voyage, Charlie Brown (and Don't Come Back!) that I watched a lot when I was younger. At one part in the movie, Snoopy is driving a car and the car gets rear-ended. The drivers of the other cars start yelling at him, and as Marcie is saying stuff to them in French--as the characters were in France in this movie--Snoopy is making all sorts of hand gestures at them, including swiping under his chin. When I was a kid, I had no idea what that meant, and just thought he was being funny. I even did that to someone in fifth grade at lunch, and was surprised when he got all outraged and told the lunch lady what I'd done. Years later, I learned that what I'd done was the Italian equivalent of raising the middle finger. Whoops.