Over sharing/attention seeking. I know someone who posted on FB from the ambulance when her daughter was hit by a car. My cousin posted about my Uncle passing not 10 minutes after it happened. My sister and her husband posted hourly blow by blow accounts of his sister dying and my sister was furious that I never responded on FB. There are just some lines that shouldn't be crossed IMHO. My kid is in the ER or my loved ones are taking their last breathes FB is going to be the last thing on my mind. These types of things warrant a phone call or at the very least a private message to loved ones. If you're giving real time updates on FB your attention really isn't on the matter at hand.
Just to be clear, I'm talking serious situations here, not something that is minor or silly.