On Pinterest, anyone can follow you if your pinned content is interesting. You may not like some Pinterest users, but there is nothing you can do to stop them from following you except to block them. Note that blocking is an extreme measure. Blocked people can't follow you or interact with your pins in any way; you can't follow them either. Previous follows and comments between you and the blocked person are automatically deleted. Note that previous pins and likes are not deleted, but you can remove them manually.
Blocking Pinterest Users
Navigate to the profile of the follower you wish to block and then click the flag in the lower-right corner of the profile information box to expand the Report menu. Click the "Block" button and then click "Block" again to confirm. The follower is blocked immediately without warning. To unblock someone, navigate to his profile and click the "Unblock" button.