Someone who 1) posts all the time and 2) in a way that’s designed to get as much attention as possible. That could be “sexy” selfies, like cleavage for girls or the slightly lifting the shirt to show off abs shot for guys. Or it could be stuff like, “oh woe, I think I might be getting fired from my job, when I JUST started it because the last one was so unfair, plus my gout is acting up and my dog ran away,” where it’s a new tale of tragedy and hardship every week. Or the dreaded combo of posting a fitness selfie and saying “I look so faaaaaaaat hereeeeeeee,” etc.
Basically when there’s a ton of it and they’re trying to manipulate people into liking them.