In today’s world where people are always offended by something silly it’s incredible that this bet is gaining popularity. I’m surprised Christians are not finding this offensive but are seeing the humor in it.
It's difficult to really tell if the large population that will involve in this bet are Christians or not, and even if Christians finds the bet offensive, what can they even do about it if not just to avoid betting on it, and do you really think it's a sin, or out of character or against the Christians religion to bet on such event? If Christians don't bet on this, there are large population of other religion that will bet and promote the bet, but we the Christians already know that jesus is not coming in 2025.
The funny thing is, even if jesus comes today, while people are making this bet, would they still get to accept that expected profit from the bookie?