This will be a narative, cos I couldn't be bothered to do the "show, don't tell" translation! :-P
So like McGarrett totally gets hit on the head and loses his memory. (Yes, this is the amnesia episode!) He escapes the hospital commando under his paper nightie tied at back, at night too, with his rock hard butt cheeks flapping in the wind. (Or was that "breaking"?)
He gets a job at a fast food where he gets his nickname, "McNuggett".
To keep up with show's bad writing and plot holes, ain't nobody recognizing him cos he shaved his beardy fuzz and wears a little paper hat while serving food. So cute. Even when Grover goes through his drive-thru window, he doesn't recognize him, though Danno (riding shotgun) does a double take. But his French fries arrive, so he focuses on stuffing his pie hole before Lou steals all his polyacrylic and propylene glycol (aka fire retardant) laced fried fries. Yup, that lethal, carcinogenic garbage is what you guys eat each time you scarf down fast food fries in USA! (Cancer does not come out of the clear blue sky, fo' crynat loud!)
Did I mention he's developed "foreign accent syndrome"? McNuggett. He's totally like "G'deiy, mei eii take yer ohohdah?" and "Wud yalak frayz wizt dat?"
McGarett (aka McNuggett) assumes a serial killer personality and develops a fixation with Hetty Lange , whom he abducts and takes to his seedy motel room. He pulls a 50 Shades of Grey on her and, after initially fighting him, Hetty (Lange) is totally like "Oh yeah, baby do me like this!"
G. Callen breaks down the door to rescue his boss but she reaches under the bed and knocks him upside the head with a cast iron frying pan, Throw Momma From The Train-style. Her torrid tryst with the disgraced one continues, and more graphically than I can type here cos the under thirteen might read, yo!
But then he's in the middle of pumpin' it and he totally regains his memory and he goes "Oh, sh... ower!" So he pulls out to take one but Hetty Lange ain't giving it up that easy, so she pulls a Psycho with a kitchen knife on him. They battle it out naked under the running shower, then McGarrett disarms her. That's when he realizes he's truly, madly in love with her so they kiss. With a lot of tongue.
Cut to them dry and back in bed, resting in each other's arms both grinning like happy idiots. Who needs a new shower now, huh!?
EPILOGUE:
White Wedding by Billy Idol plays. Beach wedding. Close up on Danno, best man smiling. The groom and bride penetrate the limo, not before a Danno/McNuggett hug: "Imma miss you man!"
*mutual manly back pats*
Annnd... they ride off into the sunset as "Just Married" on the back window fades to black!
The (2nd) Series Finale. (Though NCIS will pick it up with G . Callen having amnesia... Oh, mon Dieu!)
TRIVIA: when I wrote the above parody, I totes didn't know that there had been crossover with this other show. Psychic much?!