Can be used social situations where you want to say something absurd about a girlfriend or wife of your friends but also let them know it's non-offensive and that you're not jealous "no jello". Used as a "no homo" figure of speech.
Two dude's sitting at the pool with their wives
Dude #1: "Yo, your wife has some nice tits. No jello"
Dude #2: "Righteous, your wife has a phenomenal ass. No jello."
- OR -
Dude #1: I want to fuck your wife, no jello.
When you want to say something mean or rude about someone but in a total innocent, serious, honest and wholeheartedly way and that it has nothing to do with jealousy. And you know you're NOT jealous.
I really hate her boobs. They're way too big, really. No jello.
This man has an annoying smile, why do girls for it so much? No jello, dude.