Nocturnal Emission

Men are such perverts that they even ejaculate in their sleep. There is a perfectly normal (i.e. non-perverted) biological explanation for this, but Fiction Land likes to pretend that it's always a result of an Erotic Dream and/or A Date With Rosie Palms. Also, in Fiction Land, women never do this. (In real life, they do, but barring female ejaculation it's a lot harder for women to tell in the morning.)

If a man is discovered to have such an emission by someone else (especially his Love Interest), he will Never Live It Down.

See also Raging Stiffie and, as a natural consequence, Jizzed in My Pants.

Anime and Manga

 * Bludgeoning Angel Dokurochan mixes this with The Metamorphosis, of all things.
 * Non-sexual versions frequently happen in Wandering Son. The protagonist often has these, when his dreams are not sexual. Yuki's first flashback notes her having one of these, going to the bathroom, and her crush (now boyfriend) walks in.

Comedy

 * Serves as the basis for one of Bill Cosby's stand-up routines.

Fanfic

 * A Ranma One Half fanfiction uses this as a way for Ranma's girl side (revealed to have Ghostly Goals) to be impregnated by the male side.

Literature

 * In Lamb the Gospel According To Biff, Jesus heads to the East accompanied by his friend Biff to find the 3 wise men who came to witness his birth so he can learn how to be the messiah. The second of the wise men turns out to be a Buddhist monk who is the head of a Shaolin-esque monastery. While staying at the monastery, the two are naturally forbidden from being involved with women, or masturbating, and the only emission of semen can be involuntary, nocturnal ones. Biff, being a natural born lecher, promptly learns how to force himself to have dreams that will result in nocturnal emissions. Since they stay at the monastery for several years, he notes that he got pretty good at it.

Live-Action TV

 * In an episode of CSI involving the murder of a step-father, they find his teenaged step-son's DNA on his step-daughter's clothing and being to ask him about it. Some gentle questioning by a sympathetic and understanding Nick reveals that he's just had one of these (possibly combined with A Date With Rosie Palms) and just grabbed something to clean his hand off.
 * In The Sarah Silverman Program, Jay was in bed with Laura when she discovered he'd had a nocturnal emission. She found it so romantic because she thought this was because he'd dreamed of her, when it was in fact over the local news reporter. Then he went to work and took his anxieties out on said news reporter but then decided to explain to her about the nocturnal emission. On live TV. His girlfriend sees this and gets mad and he tries to get the news people to let him apologize. On Live TV. Then his girlfriend forgives him and when the news people actually let him apologize, she burst in, onto live TV, and delivers (in a manner not unlike a PSA) a small speech about how nocturnal emissions are involuntary and they and the dreams are not under the control of the person who has them and shouldn't be held against them.

Music

 * Suggested in Alice Cooper's "Nurse Rosetta".