Undecided questions
How to say "You're annoying" in Japanese?

annoying = 面倒くさい（めんどうくさい）

あなたはうっとうしい。
おまえうざい。(swear words)

"uzai" is appropriate in this situation, I think.

but it's a slang expression used by younger generation, so you can omit "wa" or "ga" when composing a sentence sot it fits the way you talk.

Omae uzai. or Anta uzai. is OK. (omae or anta is an impolite expression of kimi or anata)

As for "Mendou kusai", you cannot use it for people. (Some use it for that purpose though. like "Omae mendo kusai", but it's not so common.)

- omae urusai yarou dana

- urusaiyo (annoying, noisy)
uttoushiiyo (weary, annoying)
irairasurundayo (offensive, irritant, annoying)

- you need polite phrase?
urusaidesu
anata wa uttoushiidesu
anata ga iruto iraira shimasu

「迷惑（めいわく）です！！」

が一番近い表現だと思います。