Assalaamu alaykum brother. My question is the following: If i say to my friend that he is my creator, sustainer, and cherisher only to tease or just for fun, does this constitute major or minor shirk (disbelief)?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger.

There is no doubt that saying these words in reference to other than Allaah is an act of major kufr (disbelief) because it implies ascribing the attributes of Allaah to other than Him.

Hence, it is incumbent on you to repent to Allaah, The Exalted, from the sin of saying these words. You should bear in mind that uttering words of disbelief takes the same ruling whether uttered seriously or for fun. Allaah, The Exalted, says (what means): {And if you ask them, they will surely say, “We were only conversing and playing.” Say, “Is it Allaah and His verses and His Messenger that you were mocking?” Make no excuse; you have disbelieved after your belief...} [Quran 9:-65-66]

Ibn Al-ʻArabi commented on the verse 9:65 saying, “Their statements are either said seriously or in jest; in both cases it is considered an act of kufr. Kufr occurs when the person commits whatever nullifies Islam, even if done in jest, according to the consensus of all Muslims. Seriousness is closely associated with truth and knowledge, and jest is closely associated with falsehood and ignorance...” [Ahkaam Al-Quran]

There are many religious texts emphasizing the gravity of uttering statements without thoroughly thinking of them and their gravity first.

For instance, Abu Hurayrah reported that the Prophet, sallallaahu ʻalayhi wa sallam, said, “A person may utter a word thoughtlessly and, as a result of this, he will fall down into the fire of Hell deeper than the distance between the east and the west.” [Al-Bukhari and Muslim]

Fudhayl ibn ʻIyaadh said, “It is possible that the hadeeth also refers to uttering whatever involves disdain of the prophethood or the sharee'ah of Allaah, even if the sayer does not actually mean it...”

Hence, you are advised to sincerely repent to Allaah and guard your tongue against jokingly talking about matters related to Allaah, The Exalted, His verses, and His religion.

Allaah Knows best.