But this is a joke, and probably not intended to be analyzed too closely. Although this wasn't what "House" referred to, Urban Dictionary lists fifth base as anal sex.The script may have slightly changed since the 1960s.Kohl and Francoeur state that with the growing emphasis in the 1990s on safe sex to expand sex beyond heterosexual penetrative intercourse, the "home run" has taken on the additional dimension of oral sex. "I got to second base with that girl yesterday." "I didn't think I had a chance, but I made it to third base with her last night." One of the other answers has provided a nice link to the Wikipedia entry for baseball metaphors for sex.
A similar example can be found in Billy Joel's song "Zanzibar" in which he compares himself to Pete Rose and sings the lines "Me, I'm trying just to get to second base and I'd steal it if she only gave the sign.She's gonna give the go ahead, the inning isn't over yet for me." David Letterman chronicled many of these in his "Top Ten Baseball Euphemisms for Sex" — a recurring theme on the Top Ten Lists featured on the late-night talk shows he hosted before retiring in May, 2015.Among the most commonly used metaphors are the bases describing levels of physical intimacy (generally from a heterosexual perspective).Definitions vary, but the following are typical usages of the terms: The metaphors are found variously in popular American culture, with one well-known example in the Meat Loaf song "Paradise by the Dashboard Light", which describes a young couple "making out", with a voice-over commentary, by baseball announcer Phil Rizzuto, of a portion of a baseball game as a metaphor for the couple's activities.
Leman and Bell, in their book A Chicken's Guide to Talking Turkey With Your Kids About Sex, make use of it to aid parents in the discussion of puberty with their children, dividing the topics into "first base" ("Changes from the neck up"), "second base" ("Changes from the neck to the waist"), "third base" ("Changes from the waist down"), and "home plate" ("The Big 'It'").This sequence of "running the bases" is often regarded as a script, or pattern, for young people who are experimenting with sexual relationships.