What is the ruling on keeping a nickname like "My feeling is that if he passes by you, I am confident you will bow down, you will stand up, you will exalt yourself and find yourself prostrating" in a messenger application? And is there any shirk (associating partners with God) in it?

Indeed, bowing (rukūʿ) and prostration (sujūd) are acts of worship (ʿibādah) to Allah Almighty, and it is not permissible to direct them to anyone other than Allah, for that is polytheism (shirk). Allah Almighty said: "Do not prostrate to the sun or to the moon, but prostrate to Allah, who created them" [Quran 41:37], and "Bow and prostrate and worship your Lord" [Quran 22:77]. The hoopoe in the Quran disapproved of the people of Balqis prostrating to the sun, clarifying that prostration is only for Allah. And in the Hadith: "It is not befitting for a human to prostrate to a human."