What is the ruling on swearing to commit a forbidden act, and what is the ruling on uttering obscene language and its harms, and are phrases such as "Ramadan Kareem" permissible, and is one sinful for having forbidden sexual thoughts that they cannot get rid of?

If a person swears an oath concerning something unlawful, he must break the oath and offer expiation for it. Obscene language is not befitting a Muslim, and if it includes anything unlawful, then it is forbidden. Congratulating someone on the arrival of Ramadan is permissible. A person is not held accountable for evil thoughts if they overwhelm him, but he must resist them. Invoking sexual fantasies and indulging in them is impermissible.