ใจคอ My dictionary lists this as meaning "mood" and "disposition".

I have a feeling that this is a highly useful phrase, but I have never heard it used. I need to get a feel for it so that I can use it myself, and the dictionary is never very good with idioms like this.

I came across that recently in a soap story. It seems pretty straightforward as meaning disposition or mood.

แม่บ้านระเบียบก็ใจคอไม่ดี Housekeeper Rabiaps mood was not good.

"อาคุณใหญ่ ลื้อมันใจคอโหดเหี้ยมอำมหิต" Uncle Mr. Big you have a cruel and mean disposition.

Those are my translations from the examples, I'm not skilled at translating.