めちゃくちゃ

This etymology is hypothetical. Since that 無茶 (mucha) shifted to 滅茶 (mecha) by ateji (当て字), there may be an idea raised that a 滅茶 (mecha) ("ruined tea" or thus, "wrongly prepared tea") would be a 苦茶 (kucha) ("bitter tea"), which would also favor the sense of four-character idioms or 四字熟語 (yojijukugo).

• (Tokyo) めちゃくちゃ (Heiban – )^[1][2]
• IPA^(key):

めちゃくちゃ • (mechakucha) -na (adnominal めちゃくちゃな (mechakucha na), adverbial めちゃくちゃに (mechakucha ni))

1. absurd, unreasonable, illogical
2. incoherent, disorderly, messy
   • 1818, Mary Shelley, Frankenstein; or, The Modern Prometheus, Japanese translation by Giichi Shishido

     僕(ぼく)は話(はなし)をやめました。やっとのことでその人(ひと)は、めちゃくちゃな語(ご)調(ちょう)で言(い)いはじめました。

     Boku wa hanashi o yamemashita. Yatto no koto de sono hito wa, mechakucha na gochō de iihajimemashita.

     I paused; at length he spoke, in broken accents.

3. reckless, excessive
4. ruined, destroyed

• はちゃめちゃ (hachamecha)

めちゃくちゃ • (mechakucha) 

1. very, really

   めちゃくちゃ恥(は)ずかしい

   mechakucha hazukashii

   really embarrassed

   • 1914-17, Franz Kafka, The Cares of a Family Man, Japanese translation by Yū Ōkubo

     もうちょっと言(い)わせてもらうと、オドラデクはめちゃくちゃすばしっこいやつなので、どうにもつかまえられなくて、だからそういうことをどうとも言(い)えんのである。

     Mō chotto iwasete morau to, Odoradeku wa mechakucha subashikkoi yatsu na no de, dō ni mo tsukamaerarenakute, da kara sō iu koto o dō to mo ien no de aru.

     In any case, closer scrutiny is impossible, since Odradek is extraordinarily nimble and can never be laid hold of.^[3]