«عُمْرِ الْعَدُو عَلِيهْ»

This is a wish for a sick person: may they be given as many years as an enemy is expected to live. The enemy is a generic figure, not a real person, and no harm is wished on anyone. Because that enemy is imagined as long-lived, the speaker hopes the patient survives and lives on for years.

The humour rests on a traditional folk notion, not a fact, that malicious people live longer than others, as if their nastiness kept them going. The speaker grants the ailing person that same endurance while keeping all the wickedness with the enemy, so the phrase is affectionate and slightly wry.

Say it about someone who is ill, as a warm wish that they recover and outlast their sickness. Although it mentions an enemy, it is a blessing for the patient, not a curse, and not a dig at anyone.