I agree almost entirely with missred*. Granddads seem to specialize in “pull my finger,” not armpit farts. And lying about treats too close to supper time, lying about the size of the fish we caught, lying about whether I actually finished raking the yard by myself or if someone helped, etc. Also, letting us drive tractors and trucks around the farm as soon as we were (almost) tall enough to reach the pedals, or raiding Grandma’s kitchen to outfit my playhouse so that I could make mudpies decorated with elderberries (boy, was that little old woman NOT HAPPY when she discovered all of her dishes outdoors in the dirt!)
My favorite of either of my grandfathers’ funny tricks, though: My maternal grandfather was missing an index finger thanks to an accident at the lumber yard. The amputation took four bones - all three finger joints plus the metacarpal - and, unless you were really looking for something, you barely even noticed that a finger was missing. (No stump, the worst of the scar was in the webbing between the thumb and palm.) When we kids were small, and just learning to count, he’d admire our skills, and let us sit on his lap to count his fingers…
(And, when we finally figured out that Granddaddy was actually missing a finger, he explained the circumstances: “I was picking my nose and a booger bit it off!”)
Same grandfather had lost sight in one eye when he was a little kid, and had a glass eye cover for cosmetic reasons. (Of course, he almost never wore it - only when Grandmother made him, for pictures or “formal” occasions.) He also had three pretty daughters. Granddaddy was a very mild-mannered man (I literally never heard him raise his voice,) but he had his opinions. When my mother or her sisters brought home a boyfriend that didn’t meet Granddaddy’s approval, he’d wait until the couple returned home from their date, and then announce that he was going to bed, but he’d keep an eye on them… and then put his glass eye on the mantel. Apparently, a lot of teenage boys in one rural county found that downright creepy!
The great thing about granddads, though, is that they seem to let kids “reach” just a little further than parents - do things just a little beyond what Mom believes safe and age-appropriate, wander just a little farther, take a few more risks, eat a little more chocolate before dinner - and they’ve had a few years to learn to realistically assess risks and children and life in general. Plus, they know that, at the end of the day, he got to do the really fun stuff (fishing, telling jokes, etc.,) and he can send the little brats back home for baths and balanced meals and bedtimes and all of those other boring things…
*Except IME, Grandma taught card playing. And we learned to never let her keep score. She would cheat her own grandchildren at gin or rummy!