Credit: ABC Photo: Castle Hands Beckett a Drink in 3.14 "Lucky Stiff"

While all his college classmates were busy getting high, Castle was writing his first best-seller. This reminder from last night’s episode, along with the following five moments, reinforced why this guy’s easily the coolest nerd on the block.

5. Couldn’t the butler just have done it? Seriously.

Castle forgot that you can’t just arrest the butler for no reason, though think of all of the lives that might be saved if that were allowed. “How many cases have we actually had where there’s a butler as a potential suspect?” he asked Beckett. “It would be a crime if he didn’t do it.” Oh, Castle.  Once again, we were riding the same nerd wavelength as you.

4. Endorsing books... nerd books!

Granted, there are much nerdier ways to spend an afternoon than gracing back covers with your best-selling author endorsement. But the ease with which Castle does it — "A tour de force in terror," "Does for hot tubs what Jaws did for the ocean" — suggests he spends a lot of time with these books, time that could be devoted to un-nerdy stereotypes like crushing beer cans and not reading. Also, for some reason a stack of books, like over-sized glasses, will always be a "nerd prop," even though pretty much everyone has both at this point.

3. "Why does it not surprise me that you have property on the moon?"

Yep, Castle owns a few acres up there. Not just for the novelty, but for safe haven when Earth is destroyed. Beckett tried to act like she wasn’t impressed, then went home to play her guitar in a peasant blouse.

2. Castle is not "That Guy" at the club.

Doesn’t it say something that Castle owns the Ferrari, but someone else drove it? While Beckett shimmied around the club, seduced a drug dealer, and thoroughly enjoyed every single second of being undercover, Castle awkwardly ordered martinis at the bar and tried to make his way through the crowd without spilling them. It all became so clear: He’s the guy who takes time getting ready to go out, but wonders why he’s out once he gets there. Something nerdy and adorable like that.

1. Castle became a rapper.

And here was his rap:

Three armed cops
And a writer makes four
You’re under arrest
So get on the floor.

Ladies and gentleman, our best-selling author.