A person who habitually tries to stand out or be the center of attention, often with a slightly negative or teasing tone.
He's always a show-off and quickly starts cracking jokes.
That attention seeker showed up in weird clothes again.
Compound of 目立ち (continuative form of 目立つ 'to stand out') + たがり (from たがる, expressing desire) + 屋 (suffix for a person with a certain trait).