You are right coz you're not goin to America and jus focusin on polite forms which are used only in formal occasions..
But I'm not gonna be like that because every little boy can learn'em...
I'm jus using informal English for those who are eager to speak naturally like teenagers in America.
English is not jus about learning dictionary formal words...
You know what? No one has taught you slang terms that's why you think they are useless...
You're jus thinking bout settin up an institution in IRAN and talk to Iranians....
But if you're goin to have a chit-chat with a native little boy, you will be ashamed of what you have learned in Iran.