1. when 2 people unite mentally as well as physically during sex. This is implicated in the 1993 song "UMF" by Duran Duran. The terms "UMF" and "Ultimate Mind Fuck" are not in the lyrics.
2. brainwash, mass deceit, censorship, when several people (as in a cult or an entire nation) are mentally manipulated and hoodwinked and led astray by propaganda, corruption and outright lies and absolute bullshit.
2. In the 90s decade there was a lot of New Age "solutions", shilling evangelists, superstitions, comet cult suicides, Y2K hysteria and other end-of-the-millenium bullshit. Then came the 00s with all its corruption, stupidity and shit and the Iraq war circus. That's one major UMF after another!