This post may sound a bit out of place but maybe you can relate this situation to NO in your case.
One day I was talking on the phone with my girlfriend and one of my teen daughters (then) came up and asked for the car a couple times and I finally just waved her off and shook my head yes.
My BF at the time was there and said Do you know what you just did again? I was sort of bewildered as I was on the phone, so I hung up and said what did I do? He said you just gave the kids your car and didn't you just ground one of them earlier? I was like shocked because he was right.
He said I have noticed when I am here, they always ask you for things when your on the phone because they get it . I stopped to think about it and you know what it was like an awakening to me, I wanted to talk and they knew it.
So from that day on I had a little chat with them both and said from now on whatever you ask me when I am on the phone will be a no. They of course resented my friend terribley but it worked and they stested me and got No everytime, soon no more asking.
I think you can apply it the same way here with yourself. Just a story I thought I would share for No.