If you feel molested by another user, you can put them on your ignore list.
You can find this option in every message history by clicking on the dropdown arrow and there on "Ignore" or on the top right on the three dots and there you will be asked if you want to ignore the user. Under favorites or profile visitors you can also directly use the ignore button.
Alternatively, you can click on "Ignore" directly on the user's profile via the three dots. To remove a user from your ignore list, simply go to your settings and there to message filters & ignore list. There you will find all the users you have ignored.