The vilest name in Allah's sight is Malik al-Amidh (King of Kings). The narration transmitted on the authority of Shaiba (contains these words): There is no king but Allah, the Exalted and Glorious. Sufyan said: Similarly, the word Shahinshah (is also the vilest appellation). Ahmad b. Hanbal said: I asked Abu 'Amr about the meaning of Akhna. He said: The vilest.  

عَنِ النَّبِيِّ ﷺ قَالَ إِنَّ أَخْنَعَ اسْمٍ عِنْدَ اللَّهِ رَجُلٌ تَسَمَّى مَلِكَ الأَمْلاَكِ زَادَ ابْنُ أَبِي شَيْبَةَ فِي رِوَايَتِهِ لاَ مَالِكَ إِلاَّ اللَّهُ ﷻ قَالَ الأَشْعَثِيُّ قَالَ سُفْيَانُ مِثْلُ شَاهَانْ شَاهْ وَقَالَ أَحْمَدُ بْنُ حَنْبَلٍ سَأَلْتُ أَبَا عَمْرٍو عَنْ أَخْنَعَ فَقَالَ أَوْضَعَ  

The most wretched person in the sight of Allah on the Day of Resurrection and the worst person and target of His wrath would of the person who is called Malik al-Amlak (the King of Kings) for there is no king but Allah.  

عَنْ رَسُولِ اللَّهِ ﷺ فَذَكَرَ أَحَادِيثَ مِنْهَا وَقَالَ رَسُولُ اللَّهِ ﷺ أَغْيَظُ رَجُلٍ عَلَى اللَّهِ يَوْمَ الْقِيَامَةِ وَأَخْبَثُهُ وَأَغْيَظُهُ عَلَيْهِ رَجُلٌ كَانَ يُسَمَّى مَلِكَ الأَمْلاَكِ لاَ مَلِكَ إِلاَّ اللَّهُ