I just got my PS3 2 days ago, and when I beat the first boss in Demons Souls I felt pretty hardcore. Also, every minute in Army of Two with my broski.
And of course, old school ps2 splinter cell coop, me and my friend moving quickly through a room, silently picking guys off one by one, sneaking around some. I remember one time where I accidentally opened a door instead of looking through the keyhole, and a guy looked right at me, then out of the shadows behind him my partner grabbed him around the neck, and cut him. awesome.
Also in MW2 when I got a 42 kill streak.
Proof, Mcface88 Xbox live.