Looked to me like he'd gone a bit nuts some time before the movie, and was celebrating his betrayal of a user.
In the same scene, Daft Punk were paying a catchy little number for the patrons. The Bar Brawl starts, and one looks to the other, nods, and they put on something a little more appropriate.
Sam holding the lightcycle controller like a lightsaber.
Sam: What do I do with this?
Jarvis: I'll give you a hint... Not that.
And in the lightcycle battle, Sam and a conscript manage to lure one of Clu's mooks into their trap. Sam rolls by the mook and says "Boo!" as the orange program looks at the user confused. Guess what happens a few seconds later...
In the same dinner scene, Quorra's outburst of laughter when Sam mentions he dropped out of college, thinking he was joking because she couldn't even concieve of any relative of Kevin not doing well academically. Meanwhile Kevin and Sam just stare at her.
CEO:(who has no real idea) ... yeah this year we put a "12" on the box.
Right before Clu turns on Kevin, he marches into the room and yells in a bombastic, dramatic tone, demanding if Kevin believes his directive is still to create the perfect system. Kevin's response of "...Yeah?" is tinged with enough Captain Obvious to make it painfully funny.
Sam is on a first-name basis with the impound lot attendant.
Kevin Flynn was apparently cool before cool was cool:
Kevin Flynn: What's Wi-Fi?
Sam: Wireless interlinking.
Kevin Flynn: Of digital devices?
Kevin Flynn: Heh. I thought of that back in '85.
The exchange on the Encom rooftop after Sam stole the OS-12 and put it on the internet for free.
Sam: Don't sweat it, your boss is ok with it.
Guard: Yeah, the hell he is!
Sam: Your boss works for the CEO. And the CEO works for the shareholders. Now, do you know who the biggest shareholder is?
Guard: I dunno, some kid.
Sam:*gestures at himself*
Guard: *In disbelief* You're Mr. Flynn?
"I have a three-inch version of you on my shelf!" [gets disc hurled at him] "It definitely didn't do that!"
When Quorra is rescuing Sam in the Light Cycle grid, she goes to make the big jump out of the arena. Sam screams that they won't be able to make it, but she simply engages the modified engines and makes the jump, then adds a smug little "Made it." The kicker is the little shake of her head she makes as she says that; even with the helmet concealing her features, you can see the grin she's gotta be sporting.
Clu and Jarvis poking around Kevin's home, not sure of what to make of all the little elements of the real world that he has scattered around his home, like his books or chandelier. Particularly when Jarvis knocks over some glasses, and stands there frozen like a startled deer.
The whole scene where Sam tries to get his dad updated on the real world (Lakers vs. Celtics, his bike, etc.)
Sam fumbling with his disc when it bounces back to him.