" Oh stop ! You're so mellifluent " , you write to Luis, in reply to one of his posts. For starters. " mellifluent is an adjictive and your use of it, was grammatically incorrect. Mellifluous,another adj., means sweetly or smoothly; hence, your sentence really reads : " Oh stop! You're so smoothly ( or sweetly ). A second deffinition is : flowing with honey. " You're so flowing with honey " ? Is that what you REALLY meant to say to Luis ?
"You're so mellifluent," as in having a mellifluent voice, as in a pun on "fluent," as in sarcasm.
It isn't a " pun " on " fluent " at all. It is the misuse of a proper word. Stop backtacking...it doesn't wash. You misused a word, trying to be clever. It had absolutely NOTHING, whatsoever, with Luis being " fluent " in English, or any other language. You're grasping at straws ; not to mention lying through your teeth !