Let no corrupt communication proceed out of your mouth, but that which is good to the use of edifying, that it may minister grace unto the hearers. Ephesians 4:29
Being raised in a trucker's home, as a small child what I heard from my Grandpa's mouth were a lot of curses. Most times it was expressed in almost every sentence out of his mouth. An example would be "pass the #!@*# butter ". I loved him so much. This has entered my mind as a child and was and is still hard to not think of when I stub my toe or get cut off in traffic. How many of us say "Praise the Lord" when we stub our toe? It would be good I'm sure, but it is rare.
We must not judge people's spirituality on if they curse or not. God works with people in different ways. The Holy Spirit convicts people's hearts at different times, since we are all so different. God uses people in different ways and speaks through people in various manners.
An elderly couple I know were visiting a church far from their home. The preacher was a lay preacher and a new christian. As he was getting fired up in his message he began to curse. They were very shocked as I'm sure most of the congregation was. They knew he was just a new believer and said his message was still real good. I laughed when I heard about this. It's kind of a cute story. And who knows perhaps there was someone in that service who really related to the message because of the cursing.
It's probably strange for me to think this way. But you do hear testimonies of this nature. Nothing is impossible with God.