When Shepard gets a particularly bad hand injury, Art volunteers to pilot the Mako. There's a great sense of accomplishment when he gets them to the Conduit without failing. It also helps that said crowning moment of awesome is the cap of Art's development into a valuable asset on Shepard's team.
And again in Mass Vexations 2 when he comes in on an airship and proceeds to make Stuff Blow Up.
Understatement of the year. He and Jenny take the airship and fire on the mercs, blow up a warehouse and Art spends most of it screaming "Fuckers! Motherfuckers!" at anyone who can hear. Jack and Zaeed love it.
Tali's Loyalty mission is one giant CMOA for Art. After a very bad case of Poor Communication Kills with Tali, he, Thane and Kasumi steal the shuttle, fly over to the Alarei on their own, fight through all the Geth there, SAVE RAEL'ZORAH, and then come back to verbally tear the admirals a new one in an even more awesome speech than the one in the game.
Yes, this was on the funny page, but does no one else find it hilarious that a good chunk of the remaining krogan in the galaxy, are now players of The Game?
Even more amazing, considering the bottleneck the Krogan are experiencing, this is likely to become a major cultural tradition for them.
During the Rite, Grunt kills the Thresher Maw with a shotgun, much in the same way he does in one of the HD trailers for the game.
At the end of Project Overlord, Art gets to live a personal fantasy of all of us who played it and beats the shit out of Gavin, the director of the whole thing. In Canon, not even the Renegade option would allow us to do that!
Especially because Art has an autistic brother, Augie, and the thought of anyone doing such a horrific thing to their own brother makes him both furious and horrified (that, and David apparently looks a bit like Augie- it's no wonder Art snapped).
When they fight Tela Vasir, she biotically punches Tali. Art thinks something like "OK, Tela is extremely powerful... but she just punched my girlfriend. She is fucked up."