I had a fun idea that I recently tried out. The person dishing it out takes a frozen tub of ice cream with the top off and sets it upside down on the other person's head. Then they either balance it like that, or they take duct tape and tape it around the person's head, like a chin strap. Then they sit there, and the ice cream slowly melts and covers them.
I thought the condensation on the tub of ice cream would make the duct tape not stick, but it actually worked perfectly. It would probably take roughly an hour and a half to two hours to fully melt. But you can also shorten that time by thawing it out more or just moving the tub around some on the person's head. Once the ice cream gets soft, you can also just shove the tub down on their head for a satisfying smush.
It'd be a fun thing to combine with a game, humiliation role play, leaving them in an embarrassing predicament while they wait, or teasing them until the ice cream melts.
I really like this idea. But if you have the time delay, you gotta do something fun with that time. Maybe they have to complete a challenge before it melts or maybe have to just sit there during a big party?
1. Victim is tied up with the ice cream bucket on their head in someway and would have to try to get free for a prize or there would be more messy consequences.
2. A reverse concept. The victim would have to balance the ice cream in the container right side up for as long as they could until it fully melted. If they succeeded, then they got to dump it on their competitor or rival. (Or even just the melted portion if you didn't want it all or nothing). But if they failed, they would have to have the still frozen pieces put down their underwear and they'd have to complete another task that way.