No idea Fooles, but I'd guess it originated in the first Star Trek TV series. Since Spock (the Vulcan) was strongly opposed to "violence" (except when amok) it was necessary for him to participate in occasional "combat" as part of the landing teams. The pinch provided a way for him to be unbeatable without actually hurting anyone.

Speculatively, it may have fit with the overblown notion of "vulnerable spots" assaulted using ritualized "movements" as taught in the Judo, Kung Fu, et.al, that were popular before and during the early Trek period, giving "credibility" when first written into a script. (While I don't argue with the superiority of a well trained combatant, there's little "magic" to it. The guy with the biggest crowbar - or the one who shoots first - usually wins.)

"She" of the house says she believes she read somewhere that Nimoy is the one who came up with the idea; but I guess I didn't read the same fantasy. (It's inconceivable that I'd have forgotten if I'd ever read it, of course, with my steel-trap¹ mind.)

¹ old and rusty(?).

John