Has anyone ever asked you to step outside, challenging you to a fight? ~

No, but I once wound up on the fringes of a bar brawl and some guy grabbed me by the front of my shirt.  I looked him in the eye and told him if he hit me, he better make sure I don't get up.  He let go.

No, but if they did, I would say. "Go outside...if I'm not there in 15 minutes, start without me."

Once in high school.  I told her I was not going outside. I would whoop her @$$  right here. And I stepped towards her so we were nose to nose. She stepped back and I told her that was what I thought and for her to go on. 

I have found that most people will back down if they realize you will stand up. 
I have never actually gotten into a physical fight. But have bluffed myself out of a few. This post was edited by my2cents at March 5, 2021 4:44 PM MST

Yeah, I just tell 'em to stick their head up their butt and fight for air.

No.