Funniest rule change you say? Why not most effective rule change to actually make the game better? Alright, alright, I'll go with your prompt... Guess you'll have to live without my brilliant idea that would've turned hockey into an all and much improved game then! Your loss!

So for a rule change with some funny effects, I would use a drill that we used to run in our own team practice and combine it with a classic hockey excersice. You all know and hat bag skates, right? The ones coaches make their players do when they fucked up? This new rule would apply to OT and it would work like this: Every shift has to be at least a minute long and the coaches have five different "lineups" they can use for each of those shifts. Basically they can use either 0, 1, 2, 3 or 4 regular players and all the others have to do a bag skate. The coaches decide which order they go in and to predict the right match-ups against their opposition and everyone can have some fun watching at professional players struggling a lot to be useful and celebrate it when they manage to overcome the odds.