Everybody know what TV Tropes is? Technically it's like a Wikipedia for movie and television cliches (imagine an encyclopedia of variations on "jumped the shark" cliches). Depending on who you ask it's also Internet quicksand, guaranteed to cost you hours of time should you happen to stumble upon a link.
Good news! I've escaped with some Shakespeare. Specifically this idea of the "Those Two Guys" trope. Definition, you say?
Two characters, usually in a school setting, to be the mundane Greek Chorus. They may or may not be snarky and unlike the Greek Chorus, they don't break the fourth wall very often (if at all). They're completely ordinary... and no, we don't mean as in the Ordinary High-School Student, or the Badass Normal. They're ordinary. Often the best friends of the main character (who is an Ordinary High-School Student) before all the weirdness with aliens, robots, magic, demons, harems, etc.
Some pairs become involved in the plot less and less as the series progresses, especially if the plot becomes more serious. Given what usually happens to people involved in the plot, it's probably for the best. However, it's not uncommon for Those Two Guys to also become popular and even iconic characters in the series.
Their personalities usually sharply contrast, e.g. calm/hyper, jock/geek, etc., or their appearances contrast, e.g. short/tall, thin/fat... When they don't, they will be exactly the same. They might even wear Coordinated Clothes. Their names are often esoteric (either too complex or too simple to stand out), plus their non-involvement with the plot usually results in them being called "Those Two Guys".
But it wouldn't be TV Tropes without lots of examples. How about ...
Sir Toby Belch and Sir Andrew Augueface from Twelfth Night?
Trinculo and Stephano from The Tempest?
Ross and Lennox (or Lennox and Angus) from Macbeth?
Benvolio and Mercutio from ...
..wait, what? Mercutio? MERCUTIO? The page does mark this as a special case, however -- it's "somewhat off" because both of them are "somewhat relevant" to the story. Oh, well, at least they cleared that up. Somewhat.
I'm thinking they could shorten that original definition to "any two guys that typically have a scene together."
EDIT : Apparently William Shakespeare is some sort of patron saint on the site, and it is acknowledged that he in fact created most of the so-called tropes.