An obnoxious prick who posts every shitty detail of their shitty lives on facebook in the hope that one of their virtual "friends" actually gives a shit ... because none of their real "friends" would ever give a shit ....
"So and So has just arrived in America - it's so sick"
Describing somebody as a show-off carries an implicit endorsement of their capability: someone can only "show off" if they actually have something to show. An individual who seeks attention that they are not perceived to deserve is usually described much more dismissively as an attention-seeker or loudmouth
An extreme obnoxious attention starved person on facebook that posts every picture of any gift that they receive from anyone,but tries to make it "seem" they are showing appreciation for the gift when they are really just showing everyone and really saying " LOOK WHAT I GOT" In hopes of people clicking "like" and asking questions about the gift.