I don't think it's meant to be a joke, but I don't think it's right either, in English.
In modern Greek, the top poster is correct, μ IS pronounced "Me" or [Mi] (spelled as μι). Here is a YouTube video of a Greek person going through the alphabet, linked to μ. [1]
However, in English this was never used, at least not recently, and its not a "mathematicians" thing. English pronunciation of Greek letters was fixed around the 16th century (see [2] for a tiny bit of history) and was an attempt to use the classical Greek pronunciations, though probably not a very successful one.
If you're going to complain about μ, then hopefully you also complain about π, which in modern Greek is pronounced like "pee," not "pie," and so would make π-day very different...
