I was working security in an art museum when I noticed a gentleman pointing at a 19th century oil with his finger almost touching the surface. I walked over and asked him politely (but firmly) to stay back from the art. Without moving his hand he turned to look at me and said “It’s okay, I am an artist.”
I had heard this one so many times that I was ready to retaliate, and this time I did. I pulled a pencil out of my pocket and held the point as close to his eye as his finger was to the painting and said “It’s okay, I am a writer.”
Then he got the idea and backed up.