nagging is when a site prompts you out of the blue to go do something for the site, like update your profile.
Don't do this. Don't nag the user. It's annoying and disrespectful of their time.
Facebook started to display (at least since 2015-07-16) an "Update Your Profile" box and message with a weird flower graphic when you view your own profile if they determine that you should update parts of it (for whatever reason).
Note the absence of a close box or any way of dismissing it.
Here it is in the context of a profile: