"What is stupid about Jello during Sex? Please explain, I had a very sheltered upbringing"

It's not stupid, just "seemed like a good idea at the time" (another thread)....possibly, a bit of a let down to potential "Jello-aficionados and Jellobates".

I suspect because it is not as good as it looks, takes the focus away from the tasks at hand, (especially if you like Jello and are eating it:)

Another consideration, Jello, like many drink crystals, temporarily stain the skin....not that there is anything wrong with that.