Invented by British gamer Scikar, shellfished is a derivative of prawned, which is a derivative of pwned, itself derivative of owned.
<Gamer #1> :( My sister just stole my laptop
<Gamer #2> Rofl, unlucky
<Gamer #3> shellfished
Replace the word "shellfished" with "owned" and you'll understand where it comes from.
When a man is an asshole and he takes you out to dinner, you order lobster just for shits and giggles and to make him pay.
That guy is such an asshole. The next time he takes me to dinner he will be shellfished.