Common Japanese Phrases?

Question:

I've looked all over the web and the translations are completely different for common american phrases into Japanese.
I'm asking because my dad got a job in tokyo and i have to transfer schools for about a year and a half in japan.

I know formal japanese but i need/want to learn the slang now since im going to a new high school and like 90% of the time the people there (besides teachers of course) are going to be more informal and use more slang. I don't want to be lost or be dissed by someone and not know what they are saying. But do you know the CLOSEST translations for these words/phrases:

-Okay
-Whatever
You're so dumb (i heard bakayoru was it, but i've been told on the web that's also not used. agh this language is so confusing)
-What's up? (not o genki desu ka? the informal way)
-Weirdo
-Are you dumb
-Shut up (very rudely like if someone were to make a racist comment towards me about being korean, how would i say shut up in the rudest form?)
-That's cool
-Oh my god/gosh (yeah i know there's not a translation for it really, but anything close that everyday teens from tokyo use would be good enough; again, i've seen a LOT of translations but one after another, people said certain ones weren't used)

Also any COMMON curse words

Thanks. I know a lot of them are bad words I'm asking for but I was born in south korea and when we moved here when i was 6, people made fun of me a lot for my accent and being asian. Of course with time and practice i've learn american curse words and people left me alone. My dad told me prior that I may have some issues with being korean in tokyo, so im just getting prepared. Just in case.

No rude comments or trolling, if u have no help, then don't answer.
Any help is appreciated. Thanks again and happy thanksgiving everyone.

Answer:

Okay - Okay
Whatever - douzo.
You're so dumb - Omae kasu dana.
Weirdo - henjin, or kichigai
Are you dumb - Nanimo ieneenoka
Shut up - damarasshai!
That's cool - sorya iine.
Oh my god/gosh - Majikayo!!!!!!!! (I think it's the best translation which can be natural in every situation of OMG)


I think this works well.
other answerers got a lot of mistakes.
But you should try being polite then they won't hate
ShinOhkubo is a city where Koreans are very popular.
anyon.