Yes, but not on a human. Walking around some rural acreage my family has in Missouri a number of years back, I rounded a corner out on the property and came about ten feet from a very large cougar sunning itself next to the path.
I didn't have a clue he was even there until he growled.
I stopped, VERY slowly backed up along the trail about ten yards and once out of sight, pulled my pistol and continued slowly backing away all the way back to where I had parked my truck (about a quarter mile). I know that's not technically pulling a gun "on" the cougar, but at the distance I encountered him I figured that if I made a sudden move and he sprang, he'd be on me long before I got the pistol out of its holster.
I think I aged five years in those first few moments!
Make yourselves sheep and the wolves will eat you. - Benjamin Franklin