Ten with a Two

The term "beer goggles" is slang for the phenomenon in which consumption of alcohol lowers sexual inhibitions to the point that the intoxicated person uses little to no discretion when approaching or choosing sexual partners. Subsequently, the trope name Ten With a Two refers to the person (now sober) later regretting advancing on someone that he knows (or realizes) would be inappropriate or unattractive while sober.

In some cases, the numbering scenario comes into play, with the protagonist rating his target (regardless of success) on a scale of 1 to 10. To a sober person, a "1" would be someone who is very ugly while a "10" is the perfect, most physically attractive woman. With the "beer goggles" effect in play, usually any woman – regardless of perceived or actual physical beauty – will rate at or near the top of the scale.

The trope has found its way into the subject matter of several songs. While usually humorously applied, usually by a sober person observing an intoxicated individual approach his (usually ugly) target, it can have negative meaning as well ... especially when said person approaches an underage person.

Tested (with a "don't cause trouble with their spouses" method) by the Myth Busters, who ruled this Plausible for both men and women. (The negative overtones were pointed out by Jamie as well.)

Music

 * "Billy's Got His Beer Goggles On," a 2005 country hit by Neal McCoy, about a man who – after being dumped by his girlfriend – gets very drunk and starts approaching women at random, with every one of them the homecoming queen type (even if butt ugly). The song also humorously plays up the man's positive perception of bar fights and lights in the same bar.
 * "Don't the Girls All Get Prettier at Closing Time," a No. 1 country hit for Mickey Gilley in 1976. Here, a young man experiences the "beer goggle" effect as he becomes progressively intoxicated during a night at the tavern. At the beginning of his evening out, he only makes plays for the most attractive female patrons at the bar ("I'm lookin' for a nine, but eight could work right in"), but his standards become progressively lower as the night wears on ("A few more drinks and I might slip to a five or even four") before ending up waking up with an ugly woman (a "1") and swearing off alcohol.
 * "Ten With a Two," the trope namer, most famously recorded by Willie Nelson and included on his 1991 album, Born for Trouble. The song describes a middle-aged man who, after a night of drinking at a corner tavern, approaches an ugly woman. Because of the beer goggle effect, the woman has passed for beautiful in the man's eyes, and he retires with her to have sex. As Nelson sings, "Last night I came home at 2 with a 10, but at 10 I woke up with a 2." When it was a single in summer of 1991, the song gained some noteriety by conservative and women's groups for what they viewed as demeaning lyrics toward "less than perfect" women -- in other words, that the song was really about someone disparaging ugly women as having no social, romantic or other redeeming values.
 * Kenny Chesney recorded a cover the song, and is a track on is 2008 album Lucky Old Sun.

Western Animation

 * Family Guy: The trope usually applies to Brian (the anthropomorphic dog) after he becomes inebriated, and it plays a huge role in the 2010 episode "Quagmire's Dad." In that episode, Brian has sex with a woman named Ida ... unaware that "she" had recently had a sex change operation ... and (even better) was once the father of Brian's arch-rival, Quagmire! Upon learning of Brian's new "girlfriend," Peter and Lois laugh so hysterically they are unable to tell him the truth, but Stewie is able to reveal Ida's past; upon finding out, a now-sober Brian violently vomits and quakes, shaken by finding out who Ida really is. (Of course, none of this comes close to having to endure a brutal beating by Quagmire, who is outraged that Brian "fucked his dad." )
 * It's easy to imagine that Archer has no standards whatsoever, but he's pretty horrified when he gets drunk enough to sleep with Pam (not least because it's the best sex he's ever had). Although given how much they both Really Get Around, it was only a matter of time.