There is no doubt that joking about they religion is haram. Read in the Quran:
65. If you ask them (about this), they declare: ‘We were only talking idly and joking.’ Say: ‘Was it at Allaah ( عز و جل ), and His Ayaat (proofs, evidences, verses, lessons, signs, revelations, etc.) and His Messenger (صلى الله عليه وسلم) that you were mocking?’
66. Make no excuse; you disbelieved after you had believed. If We pardon some of you, We will punish others amongst you because they were Mujrimoon (disbelievers, polytheists, sinners, criminals)” [al-Tawbah 9:64-66]
Shaykh al-Islam Ibn Taymiyah said: This shows that mocking Allaah and His verses and signs is kufr and this verse indicates that the one who belittles the Messenger of Allaah in earnest or in jest is a kaafir. (Al-Saarim al-Maslool (2/70). )
Then ponder over the meaning of Allahu Akbar. It is an act of worship to say it. It is a means to raise yourself in rank in this life and the next. And here you are joking about it and confirming the disbelievers in their stigma of what Allahu Akbar means and is used for.
“They made not a just estimate of Allaah such as is due to Him. And on the Day of Resurrection the whole of the earth will be grasped by His Hand and the heavens will be rolled up in His Right Hand. Glorified be He, and High be He above all that they associate as partners with Him!” [al-Zumar 39:67]
“Nearly the heavens might be rent asunder from above them (by His Majesty), and the angels glorify the praises of their Lord, and ask for forgiveness for those on the earth. Verily, Allaah is the Oft‑Forgiving, the Most Merciful” [al-Shoora 42:5]