Does laughing as a courtesy to a colleague's mockery of marriage constitute ridicule of religion, knowing that it might be mockery of marriage itself or of the badness of some women, and does this act expel its perpetrator from Islam?

It is not permissible to generalize the ruling of disbelief (kufr) to someone who utters words that can bear more than one meaning. Their utterance does not constitute disbelief unless they intended to mock the religious ruling itself. Similarly, laughing at a statement is not considered disbelief. The fundamental principle is that a Muslim remains Muslim until proven otherwise with certainty, for Allah Almighty says: "But whoever opens his breast to disbelief - upon them is wrath from Allah, and for them is a great punishment" (Quran 16:106). It appears that the questioner is suffering from obsessive thoughts (waswasah), and is advised to persevere in supplication, disregard these whispers, and consult a psychiatrist.