Close to the edge of London, there's a certain roundabout with a series of large shops surrounding it. At some point in the past, one of the shops put up a fairly innocuous advertisement that happened to feature an attractive girl without an overabundance of clothing. The sign was removed about a month later after traffic incidents on that roundabout increased by about 75%.
The same thing happened with a Janet Jackson billboard sometime in the 1990s. If memory serves, it might have also been in London...
It was claimed that the Sex Sellsadvert◊ for Wonderbra would cause car accidents.
Played straight and subverted at the 2009 G20 summit. Presidents Obama and Sarkozy were on one side of the frame, and an attractive Brazilian intern on the other. Due to a trick of the still frame, it looked for all the world like the two were ogling the girl's backside. Video of the event shows that Obama was actually watching someone else's footing (they were on a staircase); Sarkozy... not so much.
Evidence for this trope in real life can be found here as well.
Taichung police has ordered the city's scantily-clad betel nut saleswomen to dress more conservatively to help reduce car accidents, it was reported. Under the new dress code, women peddling spicy chewing betel nuts at roadside stands are barred from revealing their bodies in sexy transparent clothes or soliciting business on the streets, the local TVBS station reported. Don't put on any dissipated poses such as dancing outside the sales booths, a policeman said while promoting the new dress code... Taichung police consider the so-called betel nut beauties a likely cause of traffic accidents in the central city as drivers are often diverted by saleswomen in flashy revealing clothes, the report said.
Barrister Alex McBride in his non-fiction book Defending the Guilty tells how he was assigned to handle a bail application for a junkie who was pretending to be insane. He was too inexperienced to realise he was being conned, until the junkie's stream of gibberish was interrupted by the sight of an attractive blonde lawyer bending over to pick up her pen, whereupon the junkie exclaimed: "Gawd, can I have her defending me?"
Dress reformers in the 19th c. introduced the "Bloomer costume" which consisted of a full knee length skirt over baggy trousers tied at the ankle — not exactly revealing. Yet one leading feminist abandoned the costume because whenever she addressed an audience of men they were so distracted by her ankles that they didn't hear a word she said.
Commercial airlines invented the Sexy Stewardess trope because when their original (male) flight attendants gave warnings about emergency procedures, it scared the passengers so badly that some would insist on being let off on the airstrip. Replacing their stewards with good-looking women invoked this trope, giving their (mostly male) clientele something to think about besides plane-crash statistics. Supposedly the decision to make interface voices (like the recorded warnings on a plane, for instance) female in general follows similar logic.
That's not really a case of looks; more of not appearing manly by demanding to be taken off the plane. After all, if the stewardess was traveling by air and apparently not afraid. Of course the more pretty a girl was, the more you'd want to appear macho and fearless.
It seems every other summer some city in Florida bans bikini-ed girls from performing any commercial (or charity even) activity on the road side. Often citing traffic accident increases as the reason.
Phryne(NSFW) was a courtesan in Ancient Greece, known for being inhumanly pretty. When she was accused of blasphemy, one of her lovers defended her - and won the jury by stripping her naked in front of them. Shortly thereafter, they all unanimously decided she was not guilty. As noted elsewhere, though, this was a case of Grecians having a solid belief that Beauty Equals Goodness - she was attractive, therefore she had to be good!
British Special Forces and some Army Intelligence units are trained to do long, boring, stake-out missions to gather intelligence from deep cover. This requires them to remain alert and observant for protracted periods of time, often spending hours just to gain fleeting glimpses of a targeted individual's comings and goings, and not to be distracted by irrelevant incident. Training exercises sometimes provide distractions at crucial moments - say, as the mark is leaving the premises under observation to get into a car, an attractive woman will appear on the other side of the street and open her coat, revealing herself to be completely naked underneath. If the trainee can still note the time, make of car, registration number, other occupants, if any, and the direction it heads off in, and not get caught up in the distraction, then it's a big contribution towards a pass mark. If all he sees is the naked lady, then he has failed.
An important rationale behind magicians' Lovely Assistant. Very few magicians are good enough to fool audiences looking at their every move attentively.
A Man Called Intrepid detailed a female British spy who occasionally used this trick. After seducing a German cipher clerk, she needs to steal codes from a safe. She engineers a fake sex scene with the clerk to distract patrolling guards, deliberately letting them see her wearing only a shirt and underwear and appearing to put her clothes on frantically. The guards said they were sorry and left her alone the rest of the night. (To the clerk's disappointment, she put her clothes back on and let a safecracker in.)
One urban legend claims that cheerleaders were first introduced as a distraction for the opposing team. Why they wouldn't also distract their own team is never addressed.
The Miami Floridians of the American Basketball Association had "ballgirls" that were essentially a combination of ballboys and cheerleaders. They would wear bikinis and do halftime dances in addition to helping with equipment, stat sheets, etc. They would sometimes stand under the basket when the opposing players were shooting freethrows.
There was a news story in June 2014 about two drivers in Germany getting in a car accident because one was distracted by a rather shapely woman sunbathing nude with her lower half hanging out of a window. The other driver reportedly shrugged it off as an understandable mistake once the woman was pointed out.