Here's an easy one: On their first real "date" back in college, Walter and Patty go see an old Greek movie called The Fiend of Athens. Here's how Patty remembers it going:
[T]he plot of The Fiend of Athens concerned a mild-mannered accountant with horn-rimmed glasses who is walking to work one morning when he sees his own picture on the front page of a newspaper, with the headline FIEND OF ATHENS STILL AT LARGE. Athenians in the street immediately start pointing at him and chasing him, and he's on the brink of being apprehended when he's rescued by a gang of terrorists or criminals who mistake him for their fiendish leader. The gang has a bold plan to do something to them that he's just a mild-mannered accountant, not the Fiend, but the gang is to counting on his help, and the rest of the city is so intent on killing him, that there finally comes an amazing moment when he whips off his glasses and becomes their fearless leader – the Fiend of Athens! He says, "OK, men, this is how the plan is going to work." (2.2.577)
Well you might read that description and think to yourself, Hey, that's just like Walter. He's really timid and polite, and Patty wants nothing more than for him to be a dangerous rebel (that is, be more like Richard). But you've only got about two seconds for this thought to flash in your mind, because in the next paragraph Patty pretty much says exactly that, imagining him "whipping his glasses off like that" (2.2.578).
But still, you're thinking, Wow, that movie really could be about Walter, because the more the book goes on, the angrier he becomes, and he sure is a bit of a revolutionary. Well then Franzen goes and steals your brilliant idea by naming the final chapter of the book's third section "The Fiend of Washington." Walter finally does embrace his inner volcano, becoming the angry madman he's had boiling inside him for so long.
Luckily for him, this fate is happier than the Fiend of Athens. Although Patty seems to have tuned out the ending, in the movie the gang realizes he isn't who they thought he was and he gets killed. Walter might delicately place his rage back in the bottle, but at least he makes it out alive. (Read more about the movie here.)