It’s from the inside of a USB missile launcher, and it’s used to signal that the motor has reached the end of the line. One of them is broken, though, and the circuit is always closed.
Four pins, 6mm form factor. Momentary. Neither the broken one nor the working one actually press in at all or make a clicking sound. Judging by the working one, it seems that just nudging the nubby thing closes the circuit. I’ve never seen a button that behaves like this before.
Button is visible in the center of the picture.