I think your son is merely in his copy cat phase (it seems to never end).
I killed 2 birds with one stone when my son (now 9) uttered his first potty mouth word. I gently warned my husband several times about spending "quality time" with our son while watching TV (Sopranos, The Godfather Trilogy and other movies where every other word is for the garbage). I said "Okay, when he says his first curse word, you're gonna handle it". He assured me it wouldn't happen. It happened. I sat him in front of his father and explained the incident. Now, they both are cured.
Lisa