It should be pretty obvious to all of you what you should do about this, but here I'll say it for those of you who aren't sure: Do nothing.
Non-believers have been making fun of believers since the beginning of time. They have made fun of all prophets and all religions. We Muslims aren't special in this regard.
The Quran has the perfect example for us to follow in this situation:
Note that the verse says 'with mild words of gentleness'. You shouldn't get angry at them, but more importantly, you shouldn't laugh at them or call them stupid.وَعِبَادُ الرَّحْمَنِ الَّذِينَ يَمْشُونَ عَلَى الْأَرْضِ هَوْنًا وَإِذَا خَاطَبَهُمُ الْجَاهِلُونَ قَالُوا سَلَامًا
And the slaves of the Most Beneficent (God) are those who walk on the earth in humility and sedateness, and when the foolish address them, they reply back with mild words of gentleness. [Quran, 25:63]
It is not our job to correct their mistakes, and it is not our job to stop them from carrying out whatever it is they want to do.
Keep your dignity and do not argue with them or try to correct them. They don't deserve your attention.وَلَوْ شَاءَ اللَّهُ مَا أَشْرَكُوا وَمَا جَعَلْنَاكَ عَلَيْهِمْ حَفِيظًا وَمَا أَنْتَ عَلَيْهِمْ بِوَكِيلٍHad God willed, they would not have taken others besides Him in worship. And We have not made you a watcher over them nor are you set over them to dispose of their affairs. [Quran, 6:107]
So why did I write about this? Because I don't want to see another pointless Muslim Facebook group trying to fight this. Save your energy for better things.