"Which Restroom?" Dilemma

When a character, due to bad signs, gender ambiguity, their being transgender, disguising as a member of the opposite sex or some other issue has no idea what bathroom, changing room or other gender-specific room is suitable for them. Potentially an extremely embarrassing or awkward situation.

While this is almost always Played For Laughs in fiction, the sobering Truth in Television is that many trans, intersex, and gender-ambiguous people face this problem every day.

Examples of "Which Restroom?" Dilemma include:

Anime and Manga

In Otome wa Boku ni Koishiteru, this is what gives Mizuho the most trouble about his 'transformation' into a girl. On his/her first day in school, he/she can't work up the courage to visit the ladies' room - and since it's an all-girl school, with only female teachers, there isn't even a men's room. He/she ends up holding it in 'till he/she gets back to the dorms, where he/she... bah! Where he can make a run for the 'private' bathroom... only for Takako, his instructor in all things feminine, to swiftly lambast him for leaving the seat up... (How he managed to pee standing up while wearing an ankle-length dress is best left to imagination.)
A running gag with Hideyoshi in Baka Test.

signs read "Boy's Changing Room", "Girl's Changing Room", and "Hideyoshi's Changing Room"
Akishisa: So is Hideyoshi a new gender?

Film

The poster for Transamerica.
In a scene from the Marx Brothers' Monkey Business, Harpo stands in front of a bathroom sign that apparently reads "men". A guy enters then gets thrown out. Harpo leaves, then we see the sign reads "Women".

Literature

In Barry Williams's book Growing Up Brady he relates the following anecdote from a time he guest-starred on Mission: Impossible as a teenage king who was fleeing from assassins by dressing up as a girl.

It was uncomfortable - and only got tougher when, a couple of hours later, I desperately had to use the bathroom.
First, I had to decide which facility to use. At first I thought it might be wise to use the ladies's room, but when push came to shove I just couldn't go in. Finally, when my bladder threw up a white flag, I was forced to hike up my skirt, throw out my pride, and in my most macho posture, march into the men's room.
Naturally, Murphy's Law was running rampant, and the men's room was packed, loaded with big, burly crew members. They looked at me first in surprise, then in disgust. Homophobic anger was rising in their eyes. I nervously muttered something at them like "How 'bout them Rams?"
With that, I flicked my long hair back and locked myself in a stall.

In the Andy Griffiths book Just Tricking, one of the short stories (Copy-Cat From Ballarat) is about Andy disguised as a girl at a school dance as part of some scheme to annoy his sister Jen. At one point he needs to use the restroom, and automatically goes to the men's room, but a teacher stops him and tells him to use the ladies' instead.
A real life example is described in Barry Farber's book How To Learn Any Language, in which the author is faced with two doors labelled "Nok" and "Ferfiak". Since he never studied Hungarian, it took some linguistic detective work to figure out which door to go through. Fortunately, he was able to use his knowledge of Chinese to figure it out.
A little children's book about a talking moose attending school has the moose wondering which restroom to use.

Live-Action TV

In Little Britain, "Emily" (Eddie) Howard, the friendly neighbourhood cross dresser, goes to a swimming pool. "She" stands outside the ladies changing room for about a direction, motioning that she is about to go in, however the clerk does not give in and eventually she reluctantly gives in and storms into the male changing rooms.
In an episode of Rentaghost, one of the characters had reason to be loitering around the change rooms at a swiming pool. One of the attendants started looking at him stragely. He looked at the two signs and, being unsure of what to do and having been told to act like an 'innocent bystander', used his magical powers to create a third sign reading 'Innocent Bystanders' and headed off in that direction.
Shows up in a parody PSA, with Trey Parker and Matt Stone portraying a pair of hermaphrodites, who are confused about which restroom to use, and find a sign labeled "Hermaphrodites" pointing to a nasty bucket.
In a Pat sketch from Saturday Night Live, the man who has a crush on the gender-ambiguous Pat follows him/her/it around waiting for Pat to use a bathroom so he can find out what gender Pat is.
This happens on The King of Queens; Doug uses the restroom in an unfamiliar restaurant, and the doors both have South-Pacific-type carvings of indeterminate sex, whose only difference is in their arm positions. Naturally his first guess is incorrect.
One episode of The Benny Hill Show had Hill going into the wrong restroom after hitting his head and reading the sign as "Laddies".

Music

The point of the mock Christmas Carol "The Restroom Door Said Gentlemen".

Music Videos

The music video for Etienne de Crecy's "Am I Wrong" features a particularly bizarre version of this. The doors feature an unidentifiable object (a safety pin?) and a cow. The protagonist enters the cow room... and proceeds to Meet the Meat.

Newspaper Comics

One The Far Side strip had two outhouses with jellyfish symbols, and the caption saying "Only they know the difference."
One Private Eye cartoon just after the Anglican Church started accepting woman bishops was a woman bishop standing outside a set of toilet doors in confusion. Both of the signs were woman signs. Because bishops wear robes. And on the sign they'd look like dresses. Visual gag.
An Insanity Streak strip had a human standing in alien bar and being completely baffled by the bizarre symbols on the restroom doors.

Tabletop Games

One of the half-breed cards in Munchkin depicts this dilemma with restrooms separated by species.

Web Comics

One VG Cats strip where the cats are (for once) cooperating, trying to figure out the gender of Slippy from Star Fox - by plying it with copious amounts of soft-drinks, and then watching the bathrooms to see which of them it enters. They are thwarted, however, when it ignores both and goes to pee in the break room.
A running gag on And Shine Heaven Now is that the new member of Iscariot wants to know what bathroom the gender-ambiguous Heinkel uses. Finally answered in this strip.
Invoked in Girls with Slingshots to prove that "Aaron" is actually Erin.
Even restrooms labeled with initials can be confusing, as Wario discovers in this comic from GG-Guys. Waldo and Winnie the Pooh suffered the same fate.

Western Animation

When the title character of SpongeBob SquarePants gets lost in the bizarre town of Rock Bottom he can't read the signs over the bathroom doors, since it's written in a strange language. So he waits for someone to walk into one of them so he can tell by context. Cue gender confusion.
An subversion: in The Simpsons, Lenny goes to a '50s theme bar and the toilets are "Cool Cats" and "Squares". He goes into one, women scream, goes into the other, same thing. He is confused.
In The Grim Adventures of Billy & Mandy, Billy jumps into Mandy's body and takes over her life. In one scene, Billy goes into the men's room but is then promptly kicked out. He then went into the ladies room but ran quickly out. He then just stood outside both bathrooms refusing to go into either one.

Real Life

Several Italian restaurants have their restroom signs, quite naturally, written in Italian. It's incredibly easy to misread the Italian word "uomini" as "women", but if you do that, your hovercraft will quickly be full of eels. Similarly, there are at least some places in Ireland with restroom signs labeled in Irish: "fir" and "mna". The former means men; the latter means women.