The initial humorous or ironic aspect of the sentence "ROMEO JULIET" stems from the lack of precision or context. This sentence could hint towards the Shakespearean characters Romeo and Juliet from the famous tragedy. However, without a verb, additional details, or context, the objective or meaning remains unclear. To someone familiar with the play, it suggests a fantastically oversimplified reduction of an intricate tragedy weaving together themes of love, hatred, fate, and mortality, which could provoke a chuckle or a smirk.
The ironic aspect could come from how this phrase typically symbolizes love's highest idealism. Romeo and Juliet are often presented as the ultimate symbol of passionate but tragic love. Yet, reality often contradicts their love story, given it leads to their untimely death. Saying "ROMEO JULIET" with no further explanation and assuming it to connote romance at its best is ironically overlooking their grim fate.
From a linguistic viewpoint, the sentence is also funny because it defies the standard structure of a complete English sentence, which consists of a subject and a predicate. The combination of two proper nouns without any further elements or punctuation gives the impression that there is a mistake or misunderstanding - which can be amusing in itself.
Furthermore, another layer of irony is perceivable in the fact that Romeo and Juliet are characters from a play known for its elaborate, poetic language. "ROMEO JULIET," in its austerity and lack of grammar or syntax, contrasts sharply with Shakespeare’s ornate language style, which is also comically ironic.
Looking at it from a historical perspective, it’s humorous because the name Romeo and Juliet, instead of symbolizing tragic love, has often been used to mock overly sentimental, teenage infatuations. So, while in literature it signifies profound romance, in common parlance, it could be used to ridicule superficial or fleeting affection, making the sentence "ROMEO JULIET" funny to certain audiences.
Finally, the specific form "ROMEO JULIET"—as two capitalized words without punctuation or other indications of context or relationship—might insinuate that Juliet is the last name of a person named Romeo. This is amusing because it basically blends two characters into one, and people familiar with the play might find it funny. Also, considering that the Capulets and Montagues (the families of Romeo and Juliet) were fierce enemies, the implication that Romeo is a part of Juliet’s family is highly ironic and amusing. ROMEO JULIET