I suffer from obsessive doubts. One day I bought a religious book that had some decorations on the cover. I said to my friend, "look at this book," using an offensive word to describe its decorations. Am I considered a disbeliever due to this act?

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 is His slave and Messenger.

You must overcome such obsessive doubts and delusions that may lead you to adverse consequences.

As for describing the book with such an offensive word, if you intended to mock its contents that pertain to the Sharee‘ah, it would undoubtedly be great evil and apostasy. To confirm this, Allaah The Almighty Says (what means): {Say, "Is it Allaah and His verses and His Messenger that you were mocking?" Make no excuse; you have disbelieved after your belief. If We pardon one faction of you - We will punish another faction because they were criminals.} [Quran 9:65-66]

However, there is no blame on you if you merely intended to mock the decoration or the quality of the cover, for example.

Allaah Knows best.