I owe no one an explanation. I have used the following:
I am on a diet.
Nah, not feeling like it tonight.
I'm driving.
I am on some meds
I have places to go after
I have a headache? lol
I had a gal call me out recently on the water I had in my hand....."is that water??"
I raised the glass and said "you BETCHA!" End of conversation......
You get the idea. It's none of their business.