Short answer
Yes. Arrogance (kibr) is a major sin. The Prophet ﷺ said no one with an atom's weight of arrogance in his heart will enter Paradise, and he defined arrogance as rejecting the truth and looking down on people. Liking good clothes, or feeling glad about a blessing while thanking Allah, is not arrogance.
Kibr is haram and counted among the major sins of the heart, as is 'ujb (self-admiration). Dressing well and looking after one's appearance is permissible, and rewarded with a good intention. Dragging one's garment out of pride is a separate sin the hadith warn against.
The four schools agree on this.
Explanation
Arrogance was the first sin committed against Allah. When Iblis refused to bow to Adam, his reason was "I am better than him" (7:12). The Quran says Allah "does not like everyone self-deluded and boastful" (31:18) and "does not like the arrogant" (16:23).
The Prophet ﷺ said: "No one will enter Paradise who has an atom's weight of arrogance in his heart." A man asked: a person likes his clothes and his shoes to be nice. He replied: "Allah is beautiful and loves beauty. Arrogance is rejecting the truth and looking down on people." So the sin is in the heart and in how you treat others: refusing to accept what is right because of who said it, and treating people as beneath you because of wealth, race, family, looks or learning.
What is not arrogance? Self-respect, confidence in your abilities, pride in being Muslim ("to Allah belongs [all] honor, and to His Messenger, and to the believers", 63:8), and being happy with a blessing while thanking Allah for it. The line is crossed when you credit yourself instead of Allah and look down on others.
Scholars of the heart list cures: remember that you came from a drop of fluid and will return to dust; put your forehead on the ground in sujood; serve people with your own hands; accept the truth even from someone younger or less important than you; and greet people first. See also what are the major sins? and Islamic values.
The evidence
Quran, Surah Luqman 31:18
وَلَا تُصَعِّرْ خَدَّكَ لِلنَّاسِ وَلَا تَمْشِ فِى ٱلْأَرْضِ مَرَحًا ۖ إِنَّ ٱللَّهَ لَا يُحِبُّ كُلَّ مُخْتَالٍۢ فَخُورٍۢ ﴿١٨﴾
And do not turn your cheek [in contempt] toward people and do not walk through the earth exultantly. Indeed, Allah does not like everyone self-deluded and boastful.
Condemns arrogance and boasting.
Quran, Surah An-Nahl 16:23
لَا جَرَمَ أَنَّ ٱللَّهَ يَعْلَمُ مَا يُسِرُّونَ وَمَا يُعْلِنُونَ ۚ إِنَّهُۥ لَا يُحِبُّ ٱلْمُسْتَكْبِرِينَ ﴿٢٣﴾
Assuredly, Allah knows what they conceal and what they declare. Indeed, He does not like the arrogant.
Shows Allah does not love the arrogant.
Sahih Muslim 91
Sahih... لاَ يَدْخُلُ الْجَنَّةَ مَنْ كَانَ فِي قَلْبِهِ مِثْقَالُ ذَرَّةٍ مِنْ كِبْرٍ ...
"No one will enter Paradise who has an atom's weight of arrogance in his heart."
Shows the gravity of arrogance.
Sahih Muslim 91
Sahih... إِنَّ اللَّهَ جَمِيلٌ يُحِبُّ الْجَمَالَ الْكِبْرُ بَطَرُ الْحَقِّ وَغَمْطُ النَّاسِ ...
"Allah is beautiful and loves beauty. Arrogance is rejecting the truth and looking down on people."
Defines arrogance and shows that looking good is not part of it.
Where the ruling is recorded
- Ihya Ulum al-Din (al-Ghazali), Book on the condemnation of pride and self-admiration. Explains the kinds of arrogance and their cures.
- al-Kaba'ir (al-Dhahabi), Chapter on arrogance. Counts arrogance among the major sins.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.