Please note that by default, anyone can view your photos and videos. If you'd like to make sure only your followers see your posts, turn on private posts. Once you turn on private posts, anyone who wants to see your photos or videos will have to send you a follower request, which you can then approve or deny.
- Go to their profile by tapping at the bottom of the app and searching for their name or username
- Tap (iPhone) or the three dots (Android/Windows Phone) in the upper-right corner of their profile
- Tap Block User or Unblock User
When you block someone, that person can't view your photos/videos or search for your Instagram profile. People aren't notified when you block them.
Yes, someone you blocked can mention your username on Instagram and this mention will appear in your news feed. If you block someone and then change your username, it'll prevent them from being able to @mention you.
If you and the person you've blocked have mutual followers, the blocked person will still be able to see your likes and comments on those followers' posts.