I always found the "Mary is actually Isis" talking point funnier than "Jesus is actually Horus", as someone who actually worships Isis. "Sorry Christoids, but the Egyptians have a monopoly on the veneration of maternal figures, and to do it yourselves is literally stealing and you should give it back!"
Yeah, the idea that Christianity is "stealing" anything from other religions, as if religious beliefs are IP in the modern sense and all Zsuzsanna Budapest needs to do is hire
Bent Pixels to copryight-strike every YouTube video of "Ave Maria", has got to take the cake here--as, of course, does the analogous lazy non-criticism of the other big proselytizing religions.