What can I do if someone added me to his/her fanlist but I don't want it?

I don't think you can. Being on someone's fanlist means that they're a fan of you, not that you're a fan of them. However, you don't have to fan them back if you don't want to.

Lel i suggest getting a life and caring about such small things like seriously why would you care about something like that.? completely ridiculous and unnecessary.

You do not have to add them back or anything.

You could politely ask them to unfan you, if you really don't want it.