I'm trying to.
Don't get into the habit of calling her a moron at all, ever, under any circumstances, in that case.
If you do, it will be too easy for it to just slip out at the office and seriously harm your relationship with the CEO.
At least it would be too easy for it to slip out for me.
I think you should make a point of only ever calling her by her name.
What does she do and how has she been annoying you at work? Have she and your CEO been married for a long time or was it a workplace romance?