Why was the term, "shellbacks" used as an insult toward the turtles?
 

Throughout the OT, the villains would often call the turtles shellbacks as if it were some kind of insult.

They would say, "You shellbacks are finished" or "I'm going to get you shellbacks!"

It wasn't just Bebop and Rocksteady who said this either, but many of the one shot villains as well.

Why would shellbacks be considered an insult or racial slur against the Turtles?

Probably because it is close to the insult/racial slur "wetback" which is a insult/racial slur against Mexicans. I don't really enjoy hearing slurs in my cartoons, but this is the best assumption I could come up with.

-ms

i always thought it was a subsitute for "assholes", any cuss work can be applied

Idk man that seems a bit strong, haha. I'd say it's just an observation insult. Like for example "Ya long haired jerk!".
The turtles used similar terms against their enemies, I think Rocksteady had been refereed to as "Horn head" once or twice.

Ha that makes sense. That and the fact that Turtle freaks and meddlesome reptiles get redundant.

Well the Turtles did insult Shredder by calling him, "tin grin" and "ol' metal mouth" in several episodes.

The turtles even call Shredder "Chrome dome" in one ep, and this is after the character was created!

I admit that "tin grin" always brought a smile to my face.

When? Out of those nicknames for Shredder in Turtles Forever, I couldn't remember ANY of them being used in the show. But, that one, I vaguely recall Michelangelo saying before.
And, a make-believe "grin" to Shredder's... :P

I watched the Season 6 set recently so in one of those eps Raph or Mike calls Shredder, "Look it's 'ol metalmouth."

This is followed by Bebop and Rocksteady being called the gruesome twosome.

We all know the Turtles didn't have their proper documentation... you know Shredder.... always hittin em where it hurts...

I'm pretty sure I recall Paulsen's Raphael saying "frying-pan face" one time.

I made a similar connection when I got a little older. But I have to agree officially with Powder that it "shellback" was more of an observational insult than a racial one. Though considering the racist/intolerant themese the show introduced I wouldn't be surprised that it could be used as sort of derogatory slur.

Was it ever shown were the turtles actually got offended or flustered over having this insult thrown at them?

My personal favorite is the one time Michelanbgelo called Bebop "pork puss" LOL! :lol:

Either way, "shellback" as an insult in the show probably wouldn't have existed if "wetback" hadn't first.

Very true, just like "what the shell" wouldn't have been a phrase if "what the hell" wasn't a phrase...

-ms