Is there an idiomatic way to express 乱说 or 胡说八道 in an elegant way?

Question

Essentially, let's say that during a polite conversation, I want to remark that someone 乱说 / 胡说八道 “talks rubbish", without sounding inelegant or unrefined (没素质).

What's a good euphemism, a chengyu or some other idiomatic way that elegantly gets the point across?

Something that you could say in not-so-informal situations, e.g. during a meeting with colleagues, or while talking with a well schooled person you aren't too familiar with.

Answer 1

• Basic
  • 没有根据 unfounded
  • 不合逻辑 illogical
  • 不可信 untrustworthy
  • 没有说服力 unpersuasive
• Advanced
  • 信口开河：说话没有根据，不可靠。（嘴巴随意张开。信口：随口。开河：原为开合。）
  • 信口雌黄：不顾事实，随口乱说或妄作评论。（雌黄：Correction fluid used in ancient China）
  • 天方夜谭 (noun)：虚妄荒诞的言论。（《天方夜谭》 is the previous translation of One Thousand and One Nights《一千零一夜》. Used for unfounded speech like a mythology / fairy tale）
• Unbiased language
  I personally use 乱说 rather than 胡说 or 瞎说.
  • 胡 means foreign, e.g. 胡椒 black pepper (which is not origin in China). Although 胡 has the meaning of 乱 and beard/moustache in dictionary, I still think 胡说 is a stereotype on foreign citizens. Does foreigner's speech imply nonsense?
  • 瞎 means is offensive way to say blind. 失明 and 视觉障碍 are inclusive language. I don't think 瞎说 is appropriate.

Answer 2

The first thing comes to mind for this: 无稽之谈. Here's the dictionary definition:

groundless statement; a cock-and-bull [cock and bull] story; a false tale; a fishy story; a latrine rumour; baseless gossip [talk]; clotted nonsense; cooked-up story; fantastic talk; idle assertions; mere unsupported statements; pack of nonsense; sheer nonsense; tale of a tub; unfounded talk

Answer 3

Beside 信口开河 and 信口雌黄, 胡言亂語 (speaking nonsense) would also be appropriate.

• Both 信口开河 and 信口雌黄 mean the same. They just have different origins

• 天方夜谭 is a noun

Also: 語無倫次: to utter nonsense