Can committing minor sins reach the level of disbelief (kufr), such as a Muslim thinking of ridiculing the beard, then shaving it? Is his action considered kufr because he acted upon what crossed his mind?

We advise you to turn away from obsessive thoughts and divert your mind from them, and to occupy your time with learning and calling to Allah. Minor sins do not turn into disbelief merely by committing them. Disbelief is not incurred by mocking the beard unless the intention is to belittle and mock the religion itself. If the intention is to mock the religion, then it is apostasy, for Allah Almighty says: "Say, 'Is it Allah and His verses and His Messenger that you were mocking?' Make no excuse; you have disbelieved after your belief." However, if one mocks the person himself for other reasons, such as shortening the garment, and his intention is not to mock the religion, then it is not apostasy. And if he says that for laughter and jest, it is a reprehensible act, and its perpetrator is in danger. But if he intends to mock the religion, then it is disbelief.