First use of the slang term "Scrub"?
The slang term "scrub", when referred to a person, can mean several things. It seems like the original usage as an adjective is someone who is not good at something - video games, sports, etc. I am interested to know if the first time it was used to refer to a "guy who thinks he's cool but he's not" was in the TLC song "No Scrubs". I am not familiar with the term before that and it seems like an isolated usage.
I vividly remember the term scrubs being used in the late 1960s in high-school sports (in Texas) to refer to the players who barely made the team and would be extremely unlikely ever to appear in an actual game that wasn't already a blow-out win or loss. Often scrubs were underclassmen who were included on the team to get seasoning and on the off-chance that they might develop into useful players in future years when some of the current players would have graduated.
Robert Chapman & Barbara Kipfer, Dictionary of American Slang, third edition (1995), has this entry for the noun scrub:
scrub 1 n by 1589 A contemptible person =BUM [example omitted] 2 n by 1892 An athlete who is not on the first or varsity team; a lowly substitute {ultimately fr. scrub, "shrub, a low, stunted tree"; the quoted 1990s teenager use is an interesting survival or perhaps a revival based on the second sense}
J.S. Farmer & W.E. Henley, Slang & Its Analogues (1903) lists these known meanings of the word:
SCRUB subs. (old colloquial).—Any mean, or ill-conditioned person, or thing ; as adj. = paltry, mean ; also SCRUBBED, and SCRUBBY ; SCRUB-RACE = a contest between contemptible animals ; after FARQUHAR and The Beaux' Strategem (1707). —B. E., GROSE. [Examples omitted.] 2. (American Univ.).—A servant.
As late as Chapman & Kipfer, Dictionary of American Slang, fourth edition (2007), there is no suggestion that a scrub "thinks he's cool but he's not." Indeed, Tom Dalzell, Flappers 2 Rappers: American Youth Slang (1996) gives a decade-by-decade account of why any pretension to coolness is exceedingly unscrublike:
[College slang circa 1900:] scrub A second-rate person
[Youth slang of the 1930s:] scrub 1. A poor student 2. A member of the second team
[The 1970s and 1980s:] scrub A younger person, perhaps a freshman
[Hiphop era (1980s and beyond):] scrub Someone with no talent.
I can imagine someone who thinks he or she is cool—and who perhaps really is cool—denigrating someone else who allegedly thinks he or she is cool, by calling that person a scrub; but arguing that a scrub is fundamentally someone who thinks he or she is cool but actually isn't makes no more sense than saying that a square is fundamentally someone who thinks he or she is a trendsetter but actually isn't. In both cases the assertion goes against generations of contrary usage. In the case of scrub, the essence of the insult relates to the scrub's irrelevance and talentlessness, not to the person's false sense of coolness.
The Oxford English Dictionary has a few relevant definitions:
"A mean insignificant fellow", dated to 1589
"A hard-worked servant", dated to 1707
"A player belonging to a weaker team", dated to 1892