So I'm a jerk, I know that. I also get enjoyment in picking on my family members like my kids, husband, and my parents. Grandma is best person to pick on. I blatantly lie to her all the time and see if she believes me. This normally lasts a couple of hours or even minutes.
One story that tends to come up is when I was a teenager and I told her I am partially deaf. She was calling me and I wasn't paying attention but watching TV.
M: Didn't you hear me calling?
Me: Don't you know, I can't hear that well. I can't tell if it is on my left or right side
M: OH really (thought for a while). They didn't have those hearing tests when you were little and you were so sick.
Me: Oh yeah, sometimes I have to look at you to know what you are saying
In the background is Grandpa cracking up
D: If she was deaf, she wouldn't hear her phone on the other side of the house
I got in trouble
This time I had the corporation from Grandpa. I took the kids to a children's party and in the goodie bag was a toy sting ray that grows in water (See picture above). We put it in water for the kids to see and according to the directions it takes about 3 days to be fully grown. The grandparents came home and grandma saw it. She asked where we got it. I told her we got it at the birthday party while Diva was trying to tell her it is a sponge and it grows.
Grandpa on the other hand went in a different direction and told her it was real. She continued the conversation asking if the fish will be OK. Grandpa told her that it is a special species and that it is very dormant and just say on the bottom of the tank.
Diva on the other hand kept insisting it was a toy. This lie went on for about 24 hours until Grandma found the packaging She even asked if there was other colors and what did they eat. The rest of the day, we would bring it up. Even when we were trying to get her to drink a bloody Mary and told her it was tomato juice. My reasoning was "Well if you believed the toy sting ray was real, you could believe that was tomato juice".
Here is another view of the "sting ray"