need some help

The very first thing I would do it tell the child's father that his behavior is unacceptable and he will not be allowed to spend time with the child unless it stops. Two year olds are smart enough to know what "no" means. You need to correct him when he says a bad word. Don't make a huge deal out of it or he will say it just for the shock value. The real problem here is the father. You need to nip this in the bud. I hope you are able to make him understand that this is not cute or funny and will harm your child in the long run. Swearing is a hard habit to break.