Man Allegedly Steals 3-Foot, 40-lb Sex Toy from Las Vegas Adult Store

Here's a real jaw-dropping crime, even in Sin City -- a man making off with a humongous dildo without paying, and even though the whole caper's on camera ... it might be tough to nail this guy.

We're told the suspect struck July 14 in broad daylight, and surveillance footage shows him calmly strolling into the Deja Vu Love Boutique in Las Vegas ... and walking out with the massive sex toy slung over his shoulder.

This is not your average dildo ... it stands a whopping 3-feet tall, weighs in at an impressive 40 pounds and goes by the name Moby Dick. Not quite what Herman Melville had in mind, we're guessing, but ya get the point: the suspect is packing! Big time.

According to the police report, the guy -- whose ID was concealed by a face mask -- crammed the phallus into a white car, similar to a Dodge Caliber, and made a clean getaway.

It's a pretty lucrative haul ... Moby goes for a cool $1,200, retail.