What about mustard cookies?
Each Christmas (before 2020) we did a cookie exchange at a friend's house. Everyone bring plate(s) of cookies, people grab whatever cookies from each plate, put them in their various container, maybe sample 1 or 2 while we play games or sit around and BS. Everyone always requests my almond sugar cookies. So the plan one year was make the 5 dozen or so cookies as normal, pull out enough dough for 3 cookies, load them up with a couple tablespoons of ground mustard, put them in with the rest of the batch, and 3 people would be VERY surprised when they got home. So I did. Well, this particular year the invitations went out late, most everyone already had other parties they committed to, and it was only the hosts their two tween kids, myself and 1 other couple. Well before the exchange happens the hosts' 12 year old boy does what 12 year olds do and starts talking smack about whatever it was. I then let the adults know what my original plan was and that I have 3 cookies that are a surprise, but I think the 12 year old needs that smack talk curtailed. The parents agreed. So I goad the 12 year old and direct his smack talk and boasting towards the consumption of cookies. "I bet you can't eat 10 cookies before the night is done, no you know I don't think you can eat 5, no, you know what, I bet you can't even eat THREE cookies!" "Oh, that's easy!" "Is it a bet?" "Yeah!" "OK, but I get to pick the cookies." These things are only the diameter of a can of pop, and when I pick out the three cookies he knows he has this in the bag. Until the first bite. The **** eating grin turned to a look of horror as it crumbled in in his mouth, and the rest of us laughed. His mom and dad thought it was a pretty good lesson for him. His dad on the other hand, makes and eats some weird stuff, knowingly tries one and liked it better than the regular version.