My approach when my dad visits goes something like this:
You know, I've always wanted to have a screen door on the back of the house. How much do you think that would cost, dad? Is it hard to install? I suppose we could try it sometime this summer. Thinking about that makes me remember how badly I need to sand and paint the front door. It looks terrible. *sigh* I guess I'll just add it to the list of things we need to get done.
I know I should feel ashamed of myself on account of my dad being 75 years old and all, but I totally don't. My mom says he likes to feel needed, so I'm helping HIM out. Or something.
So this visit, I casually mentioned that the four pampas grass plants we have in the backyard are super overgrown and need to be chopped down but holy cow, it is hard work. The very next day, my dad got at it.
I came home from work that day and was all "What did you guys do today?" and my mom was all "Tell her, Donald" to my dad. And so my dad proceeds to tell me this story...
I went outside to look at your fence that is falling down (I forgot to mention the fence I told him really needed fixing) and when I lifted up one of the panels, there was a huge snake under it. I mean, that sucker was about 8 feet long (!!!!). So I went inside and Captain Carl grabbed his shot gun (WTF with the guns, Texas????) and we went looking for it but couldn't find it. So a few hours later I decided to chop down that pampas grass and when I started, that damn snake was slithering around in it. So I grabbed the matches out of my pocket and threw a match into the grass and that sucker went up in a huge fireball.
This was the point in the story where I questioned my dad why he had matches in his pocket. He never did give me a straight answer, but I suspect he intended to burn the grass from the beginning and didn't want to tell me ON ACCOUNT OF THE BURN BAN WE ARE UNDER.
For reference, this is a fully grown pampas grass.

That is what my dad set on fire. Apparently it threw a fireball high enough into the sky that a passing motorist saw it and called 911.
Fast forward 5 minutes. My dad, who has put out the fire quickly (it only burned for a minute apparently), has now retreated upstairs to work on a different project. He neglected to inform my mom and the Captain about what happened. So imagine their surprise when eight firemen storm into the backyard while the ARSON INVESTIGATOR knocked on the front door and asked them if they knew about a fire.
My mom, knowing my dad so well, had her suspicions about who was to blame and yelled upstairs to my dad "Get your ass down here, the fire dept. is here!" to which my dad replied "Oh shit."
Luckily, the arson investigator did not give him a citation. They found a shedded snake skin (OMG I hate this state sometimes) and figured he was telling the truth about the snake and asked him to maybe not light anything else on fire. My mom is still pissed though. As for me, it gave me a good story to tell and the only thing left of the plant is a about a foot of blackened grass. The snake is nowhere to be seen. I call that a successful project.