Do not show off your actions to someone who neither gives life nor causes death, and who cannot take away from you your burdens. Showing off is a tree whose only fruit is hidden association of other gods with Allah, and its root is hypocrisy. The vain one will be told on the Day of Judgement; 'Take what you consider to be the reward of your actions from those you took as your partners with Me. Look to those whom you worshipped and called on, from whom you entertained hopes and whom you feared. And know that you cannot conceal anything inside of you from Allah: you will be deceived by yourself.'
يُخَادِعُونَ اللّهَ وَالَّذِينَ آمَنُوا وَمَا يَخْدَعُونَ إِلاَّ أَنفُسَهُم وَمَا يَشْعُرُونَ
Showing off most frequently occurs in the way people glance at others, speak, eat, drink, arrive somewhere, sit with others, dress, laugh, and in the way they perform prayers, pilgrimage, jihad, recitation of the Qur'an, and all outward acts of devotion.
However, he who is sincere towards Allah, who fears Him in his heart, and who sees himself as lacking even after he has exerted himself with every effort, will find that Allah is contented with him as a result, and he will be among those whom one expects to be free from showing off and hypocrisy, provided he continues to be in that state.