Don't worry! Even in cases when another user has blacklisted you first, you still have the ability to block their access to your profile at any time. To do this:

1. visit the user's page as a guest;
2. click the "Other actions" link under the user's profile picture;
3. select "Report";
4. in the window that appears, check the "Add this person to Black list" box;
5. confirm your selection by clicking "Report".

All done! This user will not bother you anymore. How to do this on the mobile version of the website