It is not a usual expression, and it certainly isn't used by anyone I know. I can explain that this is more of a creative sentence structure, a funny expression that is meant to demonstrate mental dexterity. If you really want to determine the sentence word by word, then here goes:1) Clam- an edible mollusc usually found in the sea. 2) Clam gargling- no idea, maybe the guy looks like a clam, or gurgles like one, or gurgles because he ate a clam. You'll have to consult another person on this. 3) Tea- a popular beverage. 4) Tosser- Either the action of tossing back your head while drinking, or a quintessentially British term meaning an unpleasant (possibly effeminate) man. So, the entire sentence could just mean:" you unpleasant, effeminate tea drinking man who looks like a clam, or speaks like a person who just ate a clam." Gibberish~

It's a bit nonsensical, but clearly trying to creatively insult someone.

There is another meaning for tea tosser, but it is probably a Boston thing. Check up on the Boston Tea Party, an act of civil disobedience against the British that happened in Boston in the 18th century. That is probably what the Tea Tosser in the Simpsons meant. Then the meaning could well become:" You clam devouring people who love acts of civil disobedience and property destruction in the name of freedom". A bit more understandable, but gibberish nonetheless...

Also worth mentioning that even the most creative insults - from Shakespeare to the Simpsons - tend to conform to a pattern (cf 'cheese-eating surrender monkeys').

Woohoo~ history!