U Jelly? is an online catchphrase used as a shorthand for “you jealous?”, an inflammatory remark typically interpreted as a form of trolling in discussions and comments.
Similar to "U MAD, the phrase is typically said in a boastful manner to cause annoyance. On imageboards, the expression is often accompanied by a cartoon character wearing a smirk.
2400 out of 2400 on sat, u jelly?
Lvl 100 in lol, u jelly?