Replying to @lidja
"Let me think about" is a passive way of saying bull crap?? Really??
To my midwestern Hoosier ears it just sounds polite, and non-judgemental.
It might mean "no way, Jose' " or "bull crap", but it is hard to be certain unless you know the speaker or can read their body language, I think.
My first reading of "Let me think about that" is that the speaker just wants a bit of time to reflect and compose their thoughts about the topic in discussion.
I agree that the thinking emoji posted above, with the crunched down left eyebrow, looks a bit emotionally involved - not necessarily angry, but very thoughtful, and perhaps disagreeing.
But so what - we can't express disagreement politely any more?