I must be a terrible parent because my 4-year old has a fascination with his middle finger and I've taken advantage of that and compiled a photo album of him flipping the bird in every shot. My wife and I recently took him to see Santa and, of course, he was giving the bird while on Santa's lap. While we were laughing hysterically, parents around us were appalled. So on the way home we talked what we should do since he's going to kindergarten next year. Should we take him to a doctor to find out why he sticks his finger up all the time?
Taking your son to the doctor may not be a bad idea if you never see his finger resting in a normal position. If he just sticks his finger up at random times, the problem will most likely solve itself as he gets older. However, even though it's hilarious to see a 4-year old giving the bird, try not to laugh when you see him do it. The more you laugh the more you'll egg it on, especially when he gets to kindergarten age. My friend's 5-year old dropped an F-bomb once and his dad laughed he adopted it as his favorite word. He got sent home a lot his first month in school.