If you could turn back time and take back one action, what would it be?

What is your biggest regret in life? Is there one thing you would change if you could go back in time?
Mine might not seem like such a big one but it has haunted me for over 20 years…
I was about 6 and my (very poor) grandfather took me to the corner store. He had something like a dime to his name. He offered to use that dime to buy me a popsicle. I complained and told him I only wanted the chocolate icecream stick, which was 25 cents. He had to negotiate with the clerk to get the treat. He died not long after. I have always hated myself for being such a spoiled brat and not appreciating his kindness. I hate that I did that. I would love to take that back, say no treat was needed, hug him and tell him I love him.