You Jelly? Is a statement used to rhetorically say you jealous? You can also make a comeback on this by saying:"No, I'm jam. This is mostly used by Gamers, and nerds. (Yes there is a difference) Meant to be used on an angry or raging n00b.
Ex: I just bought a keg of beer, you jelly? Ex: Someone is driving a Dodge Charger with hydraulics, headlights, and underglow. This would be a time to say you jelly? if you were driving. Ex: I got my license. You jelly? No, I'm jam. Ex: I just burned down your house and took all your food! You jelly?