When somebody else blocks you from using your CAC (Common Access Card) to log into a computer by inserting their CAC into the computer you were going to use. This is usually done purposely but does not have to be.
Paul: *walking over to a computer requiring him to insert his CAC to log in*
Tina: *notices Paul walking towards said computer*
Tina: *quickly cuts Paul off and inserts her CAC into the computer Paul was going to use, thereby using it herself*
Tina: Well, looks like I just got the last computer in the office.
Paul: Hey, what the heck Tina, you just CAC blocked me!
Tina: *notices Paul walking towards said computer*
Tina: *quickly cuts Paul off and inserts her CAC into the computer Paul was going to use, thereby using it herself*
Tina: Well, looks like I just got the last computer in the office.
Paul: Hey, what the heck Tina, you just CAC blocked me!
by Shadow-Dude June 2, 2018