Y5B - the sun will run out in 5 billion years, Y2K was easy
NAG - sat in a client meeting once, they discussed "NAG". I asked "what is that". they said Negative Air Gap, that to the lay person (non gender specific) is a crash between vehicles, trains etc.
I first heard 'head space' a few years ago. It seemed to mean 'state of mind', for example: "I'm not sure where his head space is at the moment." The temptation to reply with "It's immediately above his 'neck space'" was almost overwhelming.
Recently I have also heard it used to mean something akin to 'a clear mind', as in "I'll need some head space to think about that." For most people using the phrase, clearing the mind should be a quick and simple task.
At a meeting two days ago, with not a computer within ten feet of the meeting, I was informed that one of the attendees was about to "download information" to me. When I asked if that meant this attendee was about to tell me something, I was met with an "of course" stare. Spare me!