Is there a way to "block" certain friends in your steam friend list.

JunkJunk_Dog​ Sounds like an issue with Steam itself, as you can only show your "currently playing" game to everyone, to just friends, or to no one:

My Profile Options: Public | Friends Only | Private
Game Details Options: Friends Only | Private

Its also possible that your friend had removed you from their Steam friends list, as you wouldn't be able to see what they're playing if their privacy setting is set to "friends only" under "game details".

Since the issue is with Steam, if you need to contact support, you would need to go through Steam's Support.