I don’t know how the tradition got started.
Any single serving of food (usually a sandwich) left unattended on the kitchen counter for short periods of time (typically, the owner was making a bathroom visit, or was answering the door) would somehow have a bite taken out of it.
It got to the point where we didn’t recognize food without a missing bite.
~VOW
That was Linus’s mother in a Peanuts strip from 1961. Great minds think alike, or something 
As soon as my kids could make their own sandwiches, their dad would beg, plead, cajole, and implore…for a tiny, tiny, tiny bite. When they handed over the sandwich he would scarf down 3/4 or more of the sandwich and then go make them a fresh sandwich!!!
This never got old.
My mother was the usual sandwich biter. The funny part, is that she didn’t really even like baloney. But traditions must be upheld!
~VOW
My parents enjoyed Christmas trickery with our presents. Things would be hidden, or need a puzzle to find, or if we had asked for something particular, in an inappropriately sized/weighted giftbox to fool us.
Example: One year I was desperate to have a mini-bike. A few weeks before Christmas, an unusually large box appeared beneath the tree. It was so heavy I could barely move it, but it wasn’t nearly big enough to hold the bike. It drove me crazy trying to puzzle out what “compensation prize” I’d gotten. I assumed they’d nixed the motorized bike for safety reasons, but had gotten something else to spare my feelings. On Christmas day, I opened it to find it full of bricks, with a poem attached that gave me clues to find the hidden bike.
I’m a parent, and in our house we had an odd suppertime tradition. Our silverware has large hollow handles and one of the forks will rattle when shaken (apparently a manufacturing defect). As long as the kids can remember, we’ve called it the “shaky fork”. Anyone lucky enough to get the shaky fork at dinner is excused from cleanup duties. This causes puzzled looks from guests when we sat for dinner. Apparently most families do not start the evening meal by seizing their forks and violently shaking them.
My family had a regular habit of disguising Christmas presents to prevent the recipient from being able to figure out what it was. I continued this with my daughter, but our tree also has, along with the presents to the cats from Sandy Claws and from them to “The Staff”, at least one present with a tag identifying it as to and from complete strangers (e.g “To darling Millicent, From Aunt Gertrude and Uncle Rufus”). My response when asked about these is “Too bad for them. It’s our present now!”.
Dad would always take which ever child to breakfast at McDonalds for their birthday before he went to work.
Grandpa always had a treat for the dogs when he came over and Gramma always had either homemade cookies or, rarely, licorice ropes when we went to their house. When the rhubarb was tall enough, us kids were always tasked with picking the leaves off so Gramma could make pie. None of that aldulterated crap with strawberries or whatever, straight rhubarb, tart and sweet.
My mother did several of the things previously mentioned, but I can add a rather odd one. When canning peaches, she would always leave a peach pit here and there. In fact, she would arrange it so that you couldn’t see the pit from the outside of the Mason jar. Whoever got the peach pit would “get to kiss the cook.” I grew up thinking this was a common sort of thing, so I will say “You get to kiss the cook!” when something odd shows up in food I’m preparing or eating.
I get blank stares.
I love all these. I like the figurine hiding, xizor !
Deliberately putting a couple of the pits in a jar of home canned peaches makes them taste “peachier.”
ANY food containing something that should have been removed during preparation always found its way to my dad’s plate. Chicken and dumplings? Daddy got the bone. Cherry pie? Daddy got the pit. It was never a question of Daddy finding a pit; it was HOW MANY pits he would find in his single slice of pie!
~VOW