1Absurd, unreasonable, or ridiculous — said critically of a demand or idea that defies reason or is impossible to satisfy. Common as 無茶な〜 and 無茶を言う.
一日で全部覚えろなんて、無茶な話だ。
Telling me to memorize it all in one day is absurd.
そんな無茶な要求は、いくら上司でも通らないよ。
Such an unreasonable demand won't fly, even coming from the boss.
予算もないのに新店舗を出せとは、無茶を言う。
Demanding we open a new store with no budget is asking the impossible.
2Rash or reckless — acting without thinking of the consequences. Often in the form 無茶をする (to do something reckless).
体調が悪いのに一人で山に登るなんて無茶だよ。
Climbing the mountain alone when you're unwell is reckless.
若い頃は無茶をして、よく怪我をしたものだ。
When I was young I did reckless things and got hurt a lot.
無理に追い越そうとする無茶な運転は事故のもとだ。
Reckless driving that forces its way past other cars causes accidents.
3Excessive, immoderate, or extreme — going far beyond reasonable limits, to the point of harming health or common sense.
無茶なダイエットを続けて、体を壊してしまった。
I kept up an extreme diet and ended up ruining my health.
新人にいきなり無茶な量の仕事をふるのはよくない。
It's not right to dump an unreasonable amount of work on a newcomer all at once.
無茶な飲み方をすると、次の日がとてもつらい。
If you drink to excess, the next day is really rough.
4Kansai-dialect adverbial usage meaning very or extremely, roughly equivalent to めっちゃ. Casual spoken language; usually written in kana.
このラーメン、むちゃうまいやん！
This ramen is insanely good!
昨日のライブ、むっちゃ盛り上がったで。
Yesterday's concert was super lively.