I've watched a player on social media post to the point it's definitely harmed him reading the comments. Some of the things that were harmful (based on negative comments):
-Post too often. (Daily, repetitive stuff)
-Parent posting on the player's behalf excessively.
-Post measurements/times that aren't in the realm of possibility when compared to published 3rd party reported measurements/times.
-Posts that question why others haven't acknowledged the poster's ability (example: Why hasn't he gotten offers?)
-Posts of schools that have offered spots to you. Some will say this is debatable and/or needs to change. I think most will agree that posting offers to different schools in the same post is definitely a bad look.
-Posts to counter the negative comments/posts you've received.
-Posts that are staged for the sake of posting.
I'm sure there are more. These are just some examples that I saw from responses/comments to original posts.