Yes I have heard JW's use vulger language...
I remember I said to a JW that some thing freaked me out, and he said "Do you realize you keep saying that word" and I said "What word is that" he said "That F word" I replied " I can say freak any time I feel like saying freak you freak and I suppose you are one of those that believe shoot means she it too"
He told the elders that I was saying F'ing this and F'ing that.