It seems like a lot of movies in recent years have scenes involving the main characters resolving (or attemp to) serious matters in the washroom. I think Ebert mentioned it once too.
My favourite ones:
The Rock (Nicholas Cage puking and agrees to go to Alcartez)
Runaway Jury (Gene Hackman and Dustin Hoffman duke it out)

Do you guys have any that you liked?

My favorite:

"Who does Number 2 work for?"

Don't know if it counts but I love the bathroom scene in Reservoir Dogs were Tim Roth has that bag of dope and the cops walk in. Even if it is just a story being told.

Jack Nicholson marking his territory in Wolf and Jerry's run-in with Buddy in Three O'Clock High come to mind.

Robocop

I don't remember there was a scene like that in Robocop? Hmmm...

When Miguel Ferrer was the bathroom talking shit about the boss to another worker in the executive bathroom.

Kubrick had a thing for the bathroom, though I can't remember if his early films feature it as much as his later works:

Lolita - Humbert (James Mason) "mourns" the death of Charlotte while soaking in the tub, and sipping a whiskey.

Dr. Strangelove - General Buck Turgidson is in the can when he gets the call about plan R (off screen); General Jack D. Ripper kills himself in his bathroom (on screen, but behind the door)

2001: A Space Odyssey - "Instructions for Zero Gravity Toilet" (not really a dramatic turn . . .)

A Clockwork Orange - Alex betrays himself to the writer, singing a familiar song while in the tub.

Barry Lyndon - Barry reconciles with a bathing Lady Lyndon; Barry hears word of his son's accident while shaving.

The Shining - Grady gives Jack his task; "Heeere's Johnny!"

Full Metal Jacket - "I AM in a world of shit."; "I'd like to stick my tube-steak into your sister. What'll you take in trade?"

Eyes Wide Shut - "You're not even looking"

Tom Arnold :
"Yeah, that's it! You show that turd who's the boss."

That's the follow on line to Groucho's quote above.

Luis Bunuel's "The Phantom of Liberty" features a dinner party where the guests eat alone in the bathroom and converse on toilets together in the dining room.

"I...corrected them..."

This category BELONGS to THE SHINING.

liar liar - um, jim carrey trying to get out of work by beating the crap outta himself?

clockwathers - seems they spend like 15-20 minutes in the bathroom throughout the movie. not terribly recent, but it has parker posey in it. how can you go wrong?

jerry maguire at cardinals camp.

kms

actually, i think we should all blame david e. kelley. apparently something is very funny about genderless bathrooms at law firms. i think 10 minutes of ally mcbeal and boston legal are spent in the potty per episode.

Alec Bladwin and James Woods in "Ghosts of Mississippi"

big

Also, from Spaceballs: "how did you get this number, this is an unlisted wall!"

In the Company of Men

The Shining...

Delbert Grady: Did you know, Mr. Torrance, that your son is attempting to bring an outside party into this situation? Did you know that?
Jack Torrance: No.
Delbert Grady: He is, Mr. Torrance.
Jack Torrance: Who?
Delbert Grady: A ******.
Jack Torrance: A ******?
Delbert Grady: A ****** cook.
Jack Torrance: How?
Delbert Grady: Your son has a very great talent. I don't think you are aware how great it is. That he is attempting to use that very talent against your will.
Jack Torrance: He is a very willful boy.
Delbert Grady: Indeed he is, Mr. Torrance. A very willful boy. A rather naughty boy, if I may be so bold, sir.
Jack Torrance: It's his mother. She, uh, interferes.
Delbert Grady: Perhaps they need a good talking to, if you don't mind my saying so. Perhaps a bit more. My girls, sir, they didn't care for the Overlook at first. One of them actually stole a pack of matches and tried to burn it down. But I... corrected them, sir. And when my wife tried to prevent me from doing my duty, I corrected her.


Jack Torrance: You were the caretaker here, Mr. Grady.
Delbert Grady: No sir, you are the caretaker. You've always been the caretaker. I ought to know, I've always been here.

Alec Baldwin and Ben Stiller in Along Came Polly.

I just noticed Alec Baldwin spends his time in washrooms a lot

Porky's

all I could think of was that Dana Carvey movie "Opportunity Knocks" when he pretends to be Bush Sr. and does that not-funny "Not gonna do it." bit

How about Reservoir Dogs? Not only does it have Harvey Keitel and Steve Buscemi in it, it also features Keitel's ill-fated attempt to adjust his troublesome hairpiece.

and the nice foreshadowing with the pink, white, and orange bottles on the counter

Not necessary important things they were talking about - but 2 girls playing their own version of "Battleship" from Harold and Kumar came to mind upon reading the topic!