Can comments on activities, My Updates posts, and Community feed posts be deleted?  

Yes.

• You can delete your own comments on activities from the desktop version of your program.
• You can delete your own comments on My Updates posts from the desktop or app versions of your program.
• Program admin users can delete any posts from their program’s My Updates feed. 
• If your organization uses the Community Feed (Feed tab on the desktop version of your program), Posts can be deleted via request through a customer’s Customer Success Team.