Roadside Wave

A character is walking along the road when a car drives past through a puddle, splashing them big-style with water. Usually used as a comedic device which adds insult to injury in the events of an already bad day, perhaps after the character wonders how it could get any worse. Often the number one cause of Doomed New Clothes, especially fancy, expensive clothes.

Not to be confused with a character sitting at a roadside, waving at passing traffic.

Examples of Roadside Wave include:

Advertising

Parodied in an advertisement for beer, where a man waiting at a bus stop realises to his horror that the driver of an approaching car is going to inflict this on him. The driver grins evilly and pushes the accelerator to the floor. The car reaches the puddle... and sinks.
Another advert for a car plays with this trope. Earlier an elderly gent was on a massive yacht with two young attractive ladies, he sails by two people windsurfing and the wake knocks them off balance. Later one of the guys windsurfing driving home sees the gent a pair or lovely, erm, ladies walking by a massive puddle. They recognise each other and the gent looks on with horror as the car speeds up only for the man to avoid the puddle.

Anime and Manga

Ed in Fullmetal Alchemist. He gets soaked, so he uses alchemy to dry off, and is immediately arrested.
A Running Gag on Ranma ½ involved Ryoga walking along and getting splashed by something. Could be a car going by, could be someone tossing used washwater out of a window, could be (and often was) an old woman watering her plants via ladle. Since cold water turns him into a pig, this was milked for all the humor value possible.
Mamimi in FLCL gets soaked by a passing motorbike in the final episode. She later gets revenge by having the terminal core eat the bike.

Comic Books

One the 'peeves' confronted by Ali Babble in the Golden Age Batman story "Ali Babble and the Fourteen Peeves". He hauls the driver out of his car and hurls him bodily into a puddle.
A Scamp story has Scamp getting completely covered in mud by a car splash, which gets him confused for a puppy that looks exactly like him, but brown. After escaping, he promptly finds a water puddle and waits for another car to go by in order to wash off.

Film

Happens to Bobcat Goldthwait's character in Scrooged.
The Mask. Outside the Coco Bongo club, right after he's been thrown (literally 'thrown') out of it.
Citizen Kane, when Kane meets Susan Alexander.
Done as a Meet Cute in the opening scene of That Touch Of Mink, with Doris Day getting splashed by a limo carrying Cary Grant.
In Jacques Tati's Mon Oncle, a truck drives through a puddle, almost completely drenching a shopkeeper. However, the bottom of his pants are still dry... which changes when the main character, Hulot, rides by on his bicycle.
In the Drew Barrymore movie Irreconcilable Differences most of the film is set in flashback, illustrating testimony during a courtroom drama. The father of Drew's character (Casey) is retelling how he met Casey's mother, and a roadside wave is freeze-framed as he interrupts himself and the shot returns to the courtroom, with his protest about retelling this detail. The attorney asks "When did you say you met miss Van Patten Brodsky?" - SPLASH!!!
Happens to Zoolander after he loses the Male Model of the Year award to Hansel (So Hot Right Now).
And to Leslie Bibb's character in See Spot Run.

Literature

Happens to Arthur early in So Long and Thanks For All The Fish.
Bert the Small Railway engine ends up on the receiving end of one of these in The Railway Series.

Live Action TV

Opening credits to Manimal.
In an episode of Knight Rider when an arrogant reporter at a dirt bike race dons some nice clothes to meet the winner at the finish line.
SCTV Had a skit called "Shower in a Briefcase", where you can clean yourself after this happens. Also available, "Blow Dryer in a Briefcase", which is Exactly What It Says on the Tin.
Dr. Kelso had a Crowning Moment of Awesome when he exacted his vengeance on Carla with this in Scrubs.
Opening credits of Sex and the City. Quite satisfying, as the uber-selfish and vain central character is the recipient.
iCarly: Happens to Carly, Sam, and Freddie in iGo To Japan.

Music

Mentioned in one verse of The Streets' "It Was Supposed To Be So Easy," as the singer waits in line for the ATM.

Western Animation

Family Guy. Lois gets splashed on by the woman that constantly beats her for the award for best piano student. Needless to say, This Means War.
- In fact, the street next to Lois is puddle-free when her rival drives up and stops a few feet behind her. As she gloats, she pulls a bucket of water out of her car which she apparently keeps just for these sorts of situations and empties it into the gutter next to Lois... thereby producing a puddle through which she can drive, and... well, you know.
Skinner in Ratatouille gets hit by one right as his Humiliation Conga is nearing its peak.
In the Trapped in TV Land episode of Teen Titans, some old dude is standing all peacefully-like in the middle of a river, fishing in the wilderness, minding his own business when a pimping red sports car streaks past from out of nowhere, splashing him in the face and scaring away the fish, followed in hot pursuit by the Titans.
In the My Little Pony Friendship Is Magic episode "Feeling Pinkie Keen," Pinkie Pie's "Pinkie Sense" tells her that Twilight Sparkle's going to need a bath. Twilight laughs at her, then is splattered with mud by Mr. Greenhooves's passing cart.
- In "Hearts and Hooves Day", during the musical number where the Cutie Mark Crusaders look for a stallion to be Cheerilee's "very special somepony", Doctor Whooves is seen doing this to Applebloom and Scootaloo.

He might do!
(If he weren't so splashy!)

Sym-Bionic Titan: Happens to Lance and Ilana when they are hitchhiking in the rain in "The Steel Foe".
Happens twice to Heloise on Jimmy Two-Shoes, when the same car that did it to her backs up and splashes her again.
Robin Hood and Little John actually do this to Prince John at the very beginning of Robin Hood shortly after stealing his carriage and clothes, leaving him only in underwear.
Happens to ____ at the very beginning of Atlantis the Lost Empire after Fenton Harcourt refuses his proposal and speeds away from the Smithsonian Institute in his car.
This happens to Tom and Jerry (and Spike) in one cartoon. The often-Bowdlerized results show the three in Blackface.