In British culture, sometimes we can't say what we would like

to, because it could be rude.

But there are many "polite" phrases which can be used to express something negative, like:

"If you say so" = I think you are completely wrong

"Do what you think is best" = I am frustrated and I don't want to discuss this further

"That's an interesting way of looking at it" = What the hell are you talking about?

"With all due respect..." = I am about to say something that disrespects you/ your opinion

"I'll let you go now/ I'll let you get on" = I am ending this conversation

"Maybe later" = No

There are many, many more examples, because in British culture there are lots of situations in which social rules may prevent someone from saying what they really think