If someone is a christian and they are having mental health issues they may be under satanic attack and actually be listening to lies and having thoughts that shouldn't be there in their mind. The best thing is to get them or invite them to focus on scripture to remind them of WHO they are in Christ.
Pray for them and show them how to rebuke these evil thoughts. When a christian knows how to submit to God and RESIST the devil then satan can no longer attack them.
If this person isn't a christian then stay away but I would pray for them anyway that they know the truth, as once they know the truth they can be set free...you didn't mention if they were and said they 'enjoyed' those thoughts, well, a christian wouldn't. A christian might have these thoughts but KNOW they are wrong and ungodly. An unbeliever in darkness may not. If that is the case shine the light so that they are drawn to Jesus instead.