Yeah it's a joke that's at least a decade old, probably over two decades old.

And one of the most important aspects of comedy is knowing your audience. If this was said to a group of linux sysadmins I guess it's not dangerous, but it's still an old joke so not going to get much of a laugh. But if it's said to people new to linux, then it can cause damage. So it's either not funny (we all heard that one before) or an asshole prank, so not funny and malicious.