Actually, you are wrong.
I know of several Apple fanboys who claim Apple products are not vulnerable to viruses yada yada yada. Over the years, I have known many of them, and they were all Apple fans, contrary to your claims.
Well, we have to be careful about our terms.
There are lots of malware types that are erroneously called viruses -- Trojans, email scams, phishing scams, keyloggers, etc. etc.
A true virus is self-sustaining, self-replicating malware that attacks the OS, inserts itself somewhere, does stuff, and then spreads itself without human help. That's what a computer virus is.
There are no "true viruses" in the wild for OS-X. There are a few laboratory curiosities, and there have been claims, but they always turn out to be something else that needs a human to download or install or replicate.
There certainly are a good number of human-vectored non-virus malwares that attack folks using OS-X. Call them something else, but they're not really viruses. It's a specific technical term, when used correctly. Do you call your car's engine a "wheel"? Okay, so don't call other types of malware a "virus".
Let's agree on this -- Apple fanboys got way too cocky years ago and some of that crap talk hasn't died out, so there probably are some die-hards who spout nonsense. There are some of those in every camp, why not in Apple's camp too.
But although they would be full of shit if they were saying Apple products are not vulnerable to malware -- that's clearly false -- they would be ALMOST correct if they are being specific about true viruses, because no one has built a successful one yet.
Why "almost"? Because it's always possible somebody will. So to claim invulnerability into the future is silly, and they shouldn't do it.
A Mac, like any computer that is permitted to install software, is vulnerable to user installed Trojans. But, Red in Blue PA, there are no successful self installing, self transmitting, self replicating OSX viruses, worm, or other malware that meets the definition of a computer virus. There have been various candidates put forward over the past sixteen years that claimed to be the "first OSX Mac virus" but none ever proved viable. They all failed for the same reason: lack of a viable vector. Most of the candidates failed because they required user involvement at some point in the process of replication, transmit ion, or installation, and were at best were mere Trojans Horse applications.
Currently there are approximately 50 known Trojan Horse applications that can affect OSX in seven distinct families in the wild, all of which OSX itself, without the assistance of any anti-virus software, will identify and warn the user if he attempts to download, install, or download any one or a variation of them. Apple is very quick in pushing out updates to the definition file when a new variant is found.
As it stands, Macs running OSX have never been infected by a virus. . . under the accepted and technical definition of a computer virus. It may happen someday, but we are still waiting for that day.