A band or singer that everyone forgets about after their hit song runs its natural course into obscurity, because they can never get back onto the charts again. Most one-hit-wonders are that way because either they can't write their own songs, or their own songs are crap.
Crossover songs and artists are sometimes mistaken for One-Hit-Wonders, because listeners outside their genre don't know who they are. Anyone unfortunate enough to make this mistake is likely to be taken to task by numerous members of the artist's following, because it takes quite a good artist to pull off a crossover hit.
Your own songs just aren't going to cut it. Go find a hit song that no one else has covered in at least 20 years, so the teen audience will think it's new, and maybe you can be a One-hit-wonder.
Right Said Fred
The Electric Prunes
One who, when smoking out with friends is usually the first to get high, usually off of his or her very first hit off of the bong, pipe, joint, etc.
That Johny's always the first of us to get blown and act all stupid. He's a one-hit-wonder.