What's a giveaway or tell that someone may be too online?

A number of tells. Here's my shortlist.

• Missing work, school, or other important obligations. Basically neglecting responsibilities.
• Preferring online interactions over face-to-face ones. On the phone all the time, even when with people.
• Anxious, irritable, or depressed when not online
• Losing track of time while online.
• Sleep deprived.
• Not sure how to answer when asked how much they're online

Don't ask how I know...